This page shows what was measured, who it was measured in, and what that does not settle.
What Silodosin does in the body
Silodosin blocks the specific receptor variant those signals use — the one the prostate is richest in — so the muscle relaxes and the channel opens.
The prostate and the neck of the bladder are wrapped in muscle held tense by nerve signals, and that tension squeezes the tube urine passes through. The gland does not shrink. The problem is that the tubes carrying semen use the same receptor variant to push their contents forward at orgasm, so blocking it well enough to help the urine stream also stops seminal emission in about one man in four. The two effects are not separable, because they are the same molecular event in two different organs.
Why people take it. A weak, slow or hesitant stream and getting up at night, caused by an enlarged prostate
What happened in people
International Prostate Symptom Score fell 6.5 and 6.3 points against 3.6 and 3.4 on placebo in the two registration trials
✎ Source-linked record
Where this came from
A person wrote this into the record with the study named beside it. No reviewer has signed it off.
The recorded finding that sits closest to something a person would notice. Written into the record, not signed off, and it carries no population or interval.
US phase 3 registration trial of silodosin 8 mg in benign prostatic hyperplasia (NCT00224120) · a recorded source, not a stored snapshot
The limit that matters most
Its adverse-event rate is the clearest illustration in this file that an on-target effect in the wrong organ is not a safety margin problem but a design consequence
Where it acts
Smooth muscle of the prostatic stroma, prostatic urethra and bladder neck — and of the seminal vesicles and vas deferens, which use the same receptor subtype
Kind of result
Symptoms and quality of life
Supervision
RNAWiki has not recorded a supervision or regulatory status for this substance.
What the registries record it as
The substance registry classes this as chemical.
FDA substance registry · CUZ39LUY82 · read 2026-08-29
Its recorded molecular formula is C25H32F3N3O4, weighing 495.53.
US prescribing information · 322ce16e-485f-4fd2-bb30-6b4776bc9e85 · read 2026-08-30
Where each sentence above came from
A person wrote this explanation into the record, with the studies named in the path below.
The recorded use, written for a reader without medical training. Not signed off.
A limit recorded against this substance. Not signed off as a reviewed claim.
The four opening statements run to 152 words.
Words this page uses
Four words worth knowing first
Chosen from what this page shows, with each one explained before the word it depends on.
Placebo
A placebo is a dummy treatment given so the real one can be compared with it.
A picture of it, and where the picture fails
A placebo is like a blank control in an experiment.
Where that stops being true. A blank does nothing. People given a placebo often do get better.
What people get wrong. A placebo effect is read as imaginary. The improvement is measured and real.
An inactive intervention matched in appearance to the test intervention, used to control for non-specific effects.
Comparator
A comparator is whatever the treatment was measured against.
A picture of it, and where the picture fails
It is like the other runner in a race.
Where that stops being true. A race has one winner. A study can show both arms improved.
What people get wrong. Results are read without asking what the other group got. Beating nothing is not beating a treatment.
The control condition against which the experimental intervention is assessed.
Randomisation
Randomisation means chance decides who gets which treatment.
A picture of it, and where the picture fails
It is like a coin toss deciding the groups.
Where that stops being true. A coin toss is fair once. Fairness here comes from doing it for everyone.
What people get wrong. It is thought to make groups identical. It makes them similar on average, including on things nobody measured.
Allocation of participants to arms by a chance process, so that unmeasured factors are balanced in expectation.
What happened in people◇Read from sources, not yet reviewed
What happened in people
Each card is one study: the exact question it asked, who was in it, and whether it showed what it set out to show.
Change from baseline in International Prostate Symptom Score total at 12 weeks
Pooled across the two registration studies, IPSS fell 6.5 and 6.3 points against 3.6 and 3.4 on placebo, with peak flow rising 2.2 to 2.9 mL/sec against 1.2 to 1.9
Repeated elsewhere
Replicated
What this does not prove. Meeting one endpoint in one population does not carry to other goals or other people.
The limits of this study, and where it came from
Main limit. Retrograde or absent ejaculation occurred in 28.1% of 466 silodosin patients against 0.9% of 457 on placebo across the pooled programme. A later analysis found 82% of those events were absence of seminal emission rather than retrograde flow.
How far it carries. This study is recorded from the curated record, not from the registry match.
Form and route. Oral capsule, once daily with a meal
Interval reported. Not recorded in this summary
Written into the record, not signed off as a reviewed claim.
Passage of all stones 52% on silodosin against 44% on placebo, p=0.2. Distal ureteric stones passed significantly more often on silodosin, p=0.01, in an analysis for which no sample size was calculated.
Repeated elsewhere
Unreplicated
What this does not prove. A study that did not show an effect does not show that no effect exists anywhere.
The limits of this study, and where it came from
Main limit. The intent-to-treat population was below the calculated sample size, 232 against 240. No significant differences were seen in emergency-room visits, hospital admission or analgesic use.
How far it carries. This study is recorded from the curated record, not from the registry match.
Form and route. Oral capsule, once daily with a meal
Interval reported. Not recorded in this summary
Written into the record, not signed off as a reviewed claim.
US phase 3 registration trial of silodosin 8 mg in benign prostatic hyperplasia (NCT00224120) · a recorded source, not a stored snapshot
US phase 3 long-term safety study of silodosin in benign prostatic hyperplasia (NCT00224133) · a recorded source, not a stored snapshot
Adverse events
✓ The study showed what it set out to show
Who was studied
Long-term safety study (NCT00224133)
How many people
661
Study design
Phase 3 open-label extension, adverse events as primary endpoint
Compared against
Not recorded for this study
Kind of result
A number that stands in for health
What was found
A safety endpoint with no efficacy hypothesis test and no placebo arm; the study describes tolerability over extended exposure rather than effect size
Repeated elsewhere
Unreplicated
What this does not prove. Meeting one endpoint in one population does not carry to other goals or other people.
The limits of this study, and where it came from
Main limit. An open-label extension cannot separate drug effect from expectation, and no placebo arm exists to subtract. It is a legitimate safety dataset and not an efficacy one.
How far it carries. This study is recorded from the curated record, not from the registry match.
Form and route. Oral capsule, once daily with a meal
Interval reported. Not recorded in this summary
Written into the record, not signed off as a reviewed claim.
US phase 3 registration trial of silodosin 8 mg in benign prostatic hyperplasia (NCT00224120) · a recorded source, not a stored snapshot
US phase 3 long-term safety study of silodosin in benign prostatic hyperplasia (NCT00224133) · a recorded source, not a stored snapshot
Change in baseline total score on the International Prostate Symptom Score
✗ The study did not show it
Who was studied
European symptom-score trial (NCT00359905)
How many people
1228
Study design
Phase 3 randomised, 12 weeks
Compared against
Not recorded for this study
Kind of result
A number that stands in for health
What was found
No results are posted on the registry record for this study. `endpoint met: false` records the absence of a public result, not a missed endpoint.
Repeated elsewhere
Unreplicated
What this does not prove. A study that did not show an effect does not show that no effect exists anywhere.
The limits of this study, and where it came from
Main limit. The largest registered randomised symptom-score trial of this drug, with 1,228 participants, carries no results section on the public registry record.
How far it carries. This study is recorded from the curated record, not from the registry match.
Form and route. Oral capsule, once daily with a meal
Interval reported. Not recorded in this summary
Written into the record, not signed off as a reviewed claim.
US phase 3 registration trial of silodosin 8 mg in benign prostatic hyperplasia (NCT00224120) · a recorded source, not a stored snapshot
US phase 3 long-term safety study of silodosin in benign prostatic hyperplasia (NCT00224133) · a recorded source, not a stored snapshot
What we know
RNAWiki holds 4 written-up human studies for this substance, each with the question it asked.
How we know it
Each card names the study, the number of people and what the study set out to measure.
What this does not prove
These summaries were written by a person and have not been signed off as reviewed claims.
Why it matters
A study that failed is as informative as one that worked, and both are here.
What we still do not know
No reviewed claim exists, so no exact population, effect size or interval is published yet.
What it changes in the body◇Read from sources, not yet reviewed
The path through the body
From what a person takes to what changes. A solid line is a step measured in people. A dashed line is a step nobody has measured that way.
Start
Silodosin
What a person takes: Oral capsule, once daily with a meal.
The measurement behind this step
A conventional capsule taken with food, because absorption depends on it. There is no modified-release engineering here: silodosin solves the cardiovascular problem through receptor subtype preference rather than through a release profile, which is the opposite of alfuzosin's approach to the same problem. Dose is reduced in moderate renal impairment and the drug is contraindicated below a creatinine clearance of 30 mL/min.
Getting in
A once-daily capsule with a single clearance route
One capsule daily with a meal. The body clears it mainly through one liver enzyme and then through the kidneys, which is why severe impairment of either rules the drug out entirely.
╌╌Described, with no measurement named. No measurement is named for this step, so it is drawn as an unconfirmed link.
The measurement behind this step
Oral capsule, once daily with food. Metabolised principally by CYP3A4 with UGT2B7 conjugation, and metabolites eliminated renally. Contraindicated with strong CYP3A4 inhibitors, in creatinine clearance below 30 mL/min and at Child-Pugh 10 or above. A dedicated QT study at 8 mg and 24 mg for five days found no QTcI increase.
US phase 3 registration trial of silodosin 8 mg in benign prostatic hyperplasia (NCT00224120) · a recorded source, not a stored snapshot
Reaching the cell
It reaches the receptor from outside the muscle cell
The target sits on the outer surface of the smooth muscle cell, facing the bloodstream. The drug arrives and occupies it; nothing is transported inside.
──Measured in people. Written by a person from the study named beside the step. Not signed off as a reviewed claim.
The measurement behind this step
Alpha-1 adrenoceptors are plasma-membrane G-protein-coupled receptors with an outward-facing orthosteric pocket, so no transporter step and no intracellular accumulation is required. The same access applies wherever the receptor is expressed, including the seminal vesicles and vas deferens.
US phase 3 registration trial of silodosin 8 mg in benign prostatic hyperplasia (NCT00224120) · a recorded source, not a stored snapshot
What it acts on
It picks out one receptor variant more sharply than any rival
There are three versions of this receptor in the body. The prostate is rich in one of them, and silodosin prefers that one more strongly than any other drug in its class. That preference is the entire design.
╌╌Described, with no measurement named. No measurement is named for this step, so it is drawn as an unconfirmed link.
The measurement behind this step
The label states silodosin binds with high affinity to the alpha-1A subtype. The functional consequence is visible in two places at once: orthostatic hypotension at 2.6% against 1.5% on placebo, because the alpha-1B subtype governing vascular tone is largely spared, and retrograde or absent ejaculation at 28.1% against 0.9%, because the seminal tract runs on alpha-1A.
US phase 3 registration trial of silodosin 8 mg in benign prostatic hyperplasia (NCT00224120) · a recorded source, not a stored snapshot
The change it makes
The calcium signal holding the muscle tense collapses
Smooth muscle tension needs a continuous internal calcium signal. With the receptor blocked, that signal falls and the muscle releases — in the prostate, and in the tubes that carry semen.
╌╌Described, with no measurement named. No measurement is named for this step, so it is drawn as an unconfirmed link.
The measurement behind this step
Loss of alpha-1A-Gq/11 coupling ends phospholipase C activation, so inositol trisphosphate falls, sarcoplasmic reticulum calcium release drops and myosin light-chain kinase activity declines. Prostatic and bladder-neck smooth muscle relaxes; seminal vesicle and vas deferens smooth muscle fails to generate the coordinated emission contraction. Prostate volume is unchanged.
US phase 3 registration trial of silodosin 8 mg in benign prostatic hyperplasia (NCT00224120) · a recorded source, not a stored snapshot
What that does for a person
Nearly three points of symptom score, and no semen in one man in four
The symptom score improves by about three points more than placebo and the flow rate by about one millilitre a second. Roughly 28% of men stop producing semen at orgasm. Those who do are more likely to be the ones whose symptoms improved.
──Measured in people. Written by a person from the study named beside the step. Not signed off as a reviewed claim.
The measurement behind this step
IPSS fell 6.5 and 6.3 against 3.6 and 3.4 on placebo; peak flow rose 2.2 to 2.9 against 1.2 to 1.9 mL/sec. Retrograde or absent ejaculation 28.1% against 0.9%, of which 82% were absence of seminal emission rather than retrograde flow. Men with the effect had 1.75 times the odds of a combined 3-point symptom and 3 mL/sec flow response, P=0.0127.
US phase 3 registration trial of silodosin 8 mg in benign prostatic hyperplasia (NCT00224120) · a recorded source, not a stored snapshot
No suggested links are held for this record, so nothing is hidden from this path.
What we know
The record describes 5 steps from taking it to an effect in a person.
How we know it
Each step names the study behind it in the technical detail beside it.
What this does not prove
A change inside the body is a reason to look. It is not a result in a person.
Why it matters
A reader can see exactly where the chain stops being measured in people.
What we still do not know
No reviewed claim binds any of these steps to a named population.
What is missing or unclear◇Read from sources, not yet reviewed
Were people like you studied?
RNAWiki cannot tell whether a study fits you. It can show who was in it, and where the result stops carrying.
Who was studied
People similar to this profile were included.
Men with moderate to severe lower urinary tract symptoms attributed to benign prostatic hyperplasia, particularly where blood pressure or postural symptoms are the limiting factor and where ejaculatory function is not a priority.
Who is missing from the studies
Which groups were under-represented in the studies has not been recorded for this substance. Pregnancy, breastfeeding, children, older adults, and people with liver or kidney conditions are commonly excluded from trials; nothing here says whether they were.
What the label states about particular groups
On pediatric, the label states: “Safety and effectiveness in pediatric patients have not been established.”
US prescribing information · 322ce16e-485f-4fd2-bb30-6b4776bc9e85 · read 2026-08-30
On older people, the label states: “In double-blind, placebo-controlled, 12-week clinical studies of silodosin capsules, 259 (55.6%) were under 65 years of age, 207 (44.4%) patients were 65 years of age and over, while 60 (12.9%) patients were 75 years of age and over.”
US prescribing information · 322ce16e-485f-4fd2-bb30-6b4776bc9e85 · read 2026-08-30
On people who are pregnant, the label states: “Silodosin capsule is not indicated for use in women.”
US prescribing information · 322ce16e-485f-4fd2-bb30-6b4776bc9e85 · read 2026-08-30
On people with reduced liver function, the label states: “In a study comparing nine male patients with moderate hepatic impairment (Child-Pugh scores 7 to 9), to nine healthy male subjects, the single dose pharmacokinetics of silodosin were not significantly altered in patients with hepatic impairment.”
US prescribing information · 322ce16e-485f-4fd2-bb30-6b4776bc9e85 · read 2026-08-30
On people with reduced kidney function, the label states: “The effect of renal impairment on silodosin pharmacokinetics was evaluated in a single dose study of six male patients with moderate renal impairment and seven male subjects with normal renal function.”
US prescribing information · 322ce16e-485f-4fd2-bb30-6b4776bc9e85 · read 2026-08-30
Where the result stopped carrying
The primary endpoint of the ureteric-stone trial, at 52% against 44%, p=0.2, in a population slightly below the calculated sample size
The public reporting of NCT00359905, a 1,228-participant randomised symptom-score trial with no results posted
Ejaculatory function in 28.1% of men treated, which is not a failure of the drug but a failure of the premise that selectivity means safety
This is a scope explorer, not a diagnosis engine.
It shows who was studied so you can see whether people similar to you were included.
RNAWiki cannot tell whether a study fits you. It can show who was in it.
What it would be like to take◇Read from sources, not yet reviewed
Why it might seem to do nothing
A real effect and a noticed effect are different things. These are the recorded reasons the two come apart.
It was studied in different people
The people in the studies were not much like the reader.
On this record: Which groups were under-represented in the studies has not been recorded for this substance. Pregnancy, breastfeeding, children, older adults, and people with liver or kidney conditions are commonly excluded from trials; nothing here says whether they were.
The evidence may simply be wrong
Small early studies often do not hold up.
On this record: RNAWiki has not yet published a reviewed conclusion for this use.
Other reasons RNAWiki checked and found nothing for (11)
It was studied for a different goal
The studies measured something else entirely. Nothing in this record points to this reason.
A different form was studied
The studied form is not the form on the shelf. Nothing in this record points to this reason.
There was nothing to correct
Where a level is already normal, topping it up may change nothing. Nothing in this record points to this reason.
Something else had to happen too
In the studies it was paired with training, a diet or another treatment. Nothing in this record points to this reason.
The change is too small to feel
A real change can still sit below what a person notices. Nothing in this record points to this reason.
Day-to-day swing hides it
Sleep, food, stress and time of day move most numbers more than this would. Nothing in this record points to this reason.
Not enough time yet
The studies ran longer than the person has waited. Nothing in this record points to this reason.
It was not taken as studied
Missed days change the result, and studies count them. Nothing in this record points to this reason.
Something else changed at the same time
Two changes at once cannot be told apart afterwards. Nothing in this record points to this reason.
The product may not be what it says
Contents of a sold product are not always what the label states. Nothing in this record points to this reason.
No recorded reason
RNAWiki has nothing stored that would explain it. Nothing in this record points to this reason.
None of these is a reason to take more. Taking more is not a step this page ever suggests.
What it would be like to take◇Read from sources, not yet reviewed
What taking it involves
The recorded facts about getting hold of it and using it. Nothing here is a suggestion about what you should do.
How it is supplied
Prescription only
❝ Quoted from a source
Where this came from
Copied from a source RNAWiki stored, with the source named.
Read from the recorded approval status.
No source is stored against this line.
Form and route
Oral capsule, once daily with a meal
✎ Source-linked record
Where this came from
A person wrote this into the record with the study named beside it. No reviewer has signed it off.
The form and route recorded on this substance.
No source is stored against this line.
Who oversees it
RNAWiki has not recorded a supervision or regulatory status for this substance.
❝ Quoted from a source
Where this came from
Copied from a source RNAWiki stored, with the source named.
No register row and no identity class settled the question.
No source is stored against this line.
What is in the pack
A conventional capsule taken with food, because absorption depends on it.
✎ Source-linked record
Where this came from
A person wrote this into the record with the study named beside it. No reviewer has signed it off.
Recorded notes on how this is sold. The rest of the recorded wording: There is no modified-release engineering here: silodosin solves the cardiovascular problem through receptor subtype preference rather than through a release profile, which is the opposite of alfuzosin's approach to the same problem. Dose is reduced in moderate renal impairment and the drug is contraindicated below a creatinine clearance of 30 mL/min.
No source is stored against this line.
Where it is registered
Regulatory records are listed in the technical disclosure at the foot of this page.
# Counted from records
Where this came from
A count of rows RNAWiki holds. It describes our records, not your body.
Register entries are stored per jurisdiction and shown with their dates.
No source is stored against this line.
Why people stop
Not recorded.
∅ Nothing recorded
Where this came from
RNAWiki holds nothing here and says so rather than guessing.
No record of why people stopped taking it is stored for this substance.
No source is stored against this line.
What it would be like to take◇Read from sources, not yet reviewed
What can go wrong
Sorted by where each line came from. A regulator's label and a report somebody sent in are not the same kind of fact.
·Worth asking a clinician aboutWritten into the record from the studies named on this page
Retrograde or absent ejaculation dominates at 28.1% against 0.9% on placebo, and is the reason most discontinuations occur. Dizziness, orthostatic hypotension and diarrhoea each occur in under 4% and separate only modestly from placebo. Contraindicated in severe renal impairment, severe hepatic impairment, with strong CYP3A4 inhibitors, and in hypersensitivity. Warnings cover orthostatic hypotension, intraoperative floppy iris syndrome in cataract and glaucoma surgery, and priapism. A dedicated QT study at three times the therapeutic dose found no increase.
Nobody counted how many people took this and were fine, so this cannot be turned into a rate.
US phase 3 registration trial of silodosin 8 mg in benign prostatic hyperplasia (NCT00224120) · a recorded source, not a stored snapshot
Over a long time. No completed tested study window is recorded, so long-term effects are not established by the registry record.
Groups the studies covered thinly. Which groups were under-represented in the studies has not been recorded for this substance. Pregnancy, breastfeeding, children, older adults, and people with liver or kidney conditions are commonly excluded from trials; nothing here says whether they were.
What is missing or unclear◇Read from sources, not yet reviewed
Does the exact form matter?
Evidence belongs to the exact thing that was tested. A different salt, a different mixture or a different preparation is a different question.
The form that was studied
Oral capsule, once daily with a meal
✎ Source-linked record
Where this came from
A person wrote this into the record with the study named beside it. No reviewer has signed it off.
The form used in the studies cited on this page.
No source is stored against this line.
What is sold
A recorded note compares this form with the others that are sold. It is kept below, word for word.
§ A fixed RNAWiki sentence
Where this came from
Wording RNAWiki always uses, not a finding about this substance.
The recorded note, unchanged: There is no modified-release engineering here: silodosin solves the cardiovascular problem through receptor subtype preference rather than through a release profile, which is the opposite of alfuzosin's approach to the same problem. Dose is reduced in moderate renal impairment and the drug is contraindicated below a creatinine clearance of 30 mL/min.
No source is stored against this line.
What is recorded as being sold
39 products list this as an active ingredient in the United States drug directory. 39 of them contain it and nothing else.
FDA National Drug Code directory · 72789-351 · read 2026-08-29
They are sold as capsule and powder, taken oral.
FDA National Drug Code directory · 72789-351 · read 2026-08-29
The regulator's established pharmacologic class for it is adrenergic alpha-antagonists [moa] and alpha-adrenergic blocker [epc].
FDA National Drug Code directory · 72789-351 · read 2026-08-29
17 published labels name it as an active ingredient. 17 of them describe this substance alone, which is where its own label text on this page comes from.
US prescribing information · 322ce16e-485f-4fd2-bb30-6b4776bc9e85 · read 2026-08-29
Those labels are classed as human prescription drug.
US prescribing information · 322ce16e-485f-4fd2-bb30-6b4776bc9e85 · read 2026-08-29
Silodosin is oral at 3 DOSAGE FORMS AND STRENGTHS The 4 mg capsules are white opaque/white opaque, hard gelatin capsules of size “3” imprinted with “A238” on cap in gold ink, filled with white to off-white powder., recorded as fda label in effect 2023-01-30 in the United States.
US prescribing information · 322ce16e-485f-4fd2-bb30-6b4776bc9e85 · read 2026-08-30
Recorded price in US: 0.2703–0.31375 USD per one unit as the pricing file counts it — a tablet, capsule, patch or single item, across 21 priced products whose strengths and pack forms differ, as of 2026-08-26, paid by retail pharmacies buying the product, as surveyed by the Centers for Medicare & Medicaid Services. It is not a list price, an insurance price, or what anyone pays at a counter..
Recorded source · 2026-08-26 · read 2026-08-28
Evidence carries across two names for one substance. It does not carry across a salt, a mirror form or a mixture.
What it would be like to take◇Read from sources, not yet reviewed
What you could measure
This one is decided with a clinician, so this section holds questions to ask rather than a plan to run.
RNAWiki could not confidently classify this substance, so no self-experiment plan is offered.
Questions worth asking
Which of the trials of Silodosin studied people like me?
What was measured, and for how long?
Was the result a laboratory value or a health outcome?
What would we watch for, and when would we stop?
Tracking can show whether something changed for you. It cannot show what caused it.
RNAWiki records evidence. It does not say whether this substance is right for you.
What is missing or unclear◇Read from sources, not yet reviewed
Claims that go past the evidence
Things said about this substance that sound reasonable, and the exact step that is missing between the evidence and the claim.
✗Goes past the evidence
That silodosin works as medical expulsive therapy for ureteric stones — the whole-ureter primary endpoint was not met and the positive finding is an unpowered subgroup
Why it sounds right. It follows from something real on this page: a body step, an animal result or a related finding.
The missing step. Nobody measured this in people for this use, or the study that did measure it did not show it.
What would change this
A study in people, for this exact use, measuring this exact thing, that a reviewer signs off.
RNAWiki has not yet published a reviewed conclusion for this use.
✗Goes past the evidence
That the ejaculatory effect is retrograde flow — 82% of the coded events were absence of seminal emission, a different physiological event
Why it sounds right. It follows from something real on this page: a body step, an animal result or a related finding.
The missing step. Nobody measured this in people for this use, or the study that did measure it did not show it.
What would change this
A study in people, for this exact use, measuring this exact thing, that a reviewer signs off.
RNAWiki has not yet published a reviewed conclusion for this use.
✗Goes past the evidence
That absent emission should be sought as a marker of adequate dosing — the association is a target-engagement observation from a post hoc responder analysis, not a dosing strategy
Why it sounds right. It follows from something real on this page: a body step, an animal result or a related finding.
The missing step. Nobody measured this in people for this use, or the study that did measure it did not show it.
What would change this
A study in people, for this exact use, measuring this exact thing, that a reviewer signs off.
RNAWiki has not yet published a reviewed conclusion for this use.
✗Goes past the evidence
That greater subtype selectivity means fewer side effects — here it means a different and far more frequent one
Why it sounds right. It follows from something real on this page: a body step, an animal result or a related finding.
The missing step. Nobody measured this in people for this use, or the study that did measure it did not show it.
What would change this
A study in people, for this exact use, measuring this exact thing, that a reviewer signs off.
RNAWiki has not yet published a reviewed conclusion for this use.
What is missing or unclear◇Read from sources, not yet reviewed
What nobody knows yet
Open questions, each with why it is open and what would close it.
Missing populations
Which groups were under-represented in the studies has not been recorded.
Why it matters. Recorded by the evidence model as a gap on this record.
What would answer it
A study that measures it, and a reviewer to sign it off.
Last checked 2026-09-04. Searched: The sources listed in the receipts at the foot of this page.
Missing long-term data
No completed tested study window is recorded.
Why it matters. Recorded by the evidence model as a gap on this record.
What would answer it
A study that measures it, and a reviewer to sign it off.
Last checked 2026-09-04. Searched: The sources listed in the receipts at the foot of this page.
No reviewed conclusion
RNAWiki has not yet published a reviewed conclusion for this use.
Why it matters. Recorded by the evidence model as a gap on this record.
What would answer it
A study that measures it, and a reviewer to sign it off.
Last checked 2026-09-04. Searched: The sources listed in the receipts at the foot of this page.
Missing interaction studies
No interaction was found in the registers checked. Not finding one is not the same as showing there is none.
Why it matters. Recorded by the evidence model as a gap on this record.
What would answer it
A study that measures it, and a reviewer to sign it off.
Last checked 2026-09-04. Searched: The sources listed in the receipts at the foot of this page.
Formulation uncertainty
Several salts, forms or products of Silodosin are recorded. Results from one form may not transfer to another.
Why it matters. Recorded by the evidence model as a gap on this record.
What would answer it
A study that measures it, and a reviewer to sign it off.
Last checked 2026-09-04. Searched: The sources listed in the receipts at the foot of this page.
Mechanism not reviewed
No reviewed mechanism story exists for this substance.
Why it matters. Recorded by the evidence model as a gap on this record.
What would answer it
A study that measures it, and a reviewer to sign it off.
Last checked 2026-09-04. Searched: The sources listed in the receipts at the foot of this page.
What happened in people◇Read from sources, not yet reviewed
Check any of this yourself
Every line above traced back to the study it came from. This is the technical layer, and the vocabulary changes here.
Every line above can be traced to the study named beside it. Follow the link and read it.
Ejaculation stops in 28.1% against 0.9% on placebo — thirty times the rate
In plain words
More than one man in four on silodosin stops producing semen at orgasm. On placebo it is fewer than one in a hundred. This is the drug working, in the wrong organ.
What was measured
Incidence of retrograde or absent ejaculation, dizziness, orthostatic hypotension and diarrhoea against placebo
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
Pooled 12-week placebo-controlled data on the US label, from 466 patients on silodosin and 457 on placebo, report retrograde ejaculation in 28.1% against 0.9%. Dizziness was 3.2% against 1.1%, orthostatic hypotension 2.6% against 1.5% and diarrhoea 2.6% against 1.3% — every other effect an order of magnitude smaller than the ejaculatory one. The mechanism is not incidental: seminal vesicle and vas deferens smooth muscle expresses the alpha-1A subtype that silodosin was designed to prefer, so the same receptor occupancy that relaxes the prostatic urethra abolishes seminal emission. The rate is dose-ordered across the class as well: tamsulosin reports 8.4% at 0.4 mg and 18.1% at 0.8 mg, and silodosin, the most alpha-1A-preferring agent, reports 28.1%.
Source
US prescribing information for silodosin capsules, Adverse Reactions section, pooled 12-week placebo-controlled studies (openFDA drug label endpoint)
Role in the trial
Not matched to a registered study
Identity check
no open identity hold
Audit mark
verified
Review state
Written into the record, not signed off as a reviewed claim
Most of the "retrograde ejaculation" was not retrograde
In plain words
The label calls the effect retrograde ejaculation, which means semen going backwards into the bladder. When the trial data were examined, 82% of the events were something different: orgasm with no seminal emission at all.
What was measured
Proportion of coded retrograde-ejaculation events that were reported as orgasm with absence of seminal emission
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
Roehrborn and colleagues analysed the two phase 3 registration studies (NCT00224107 and NCT00224120). Of 466 patients receiving silodosin, 131 (28%) reported retrograde ejaculation and 335 (72%) did not; 4 of 457 placebo patients (0.9%) reported it. Of 134 such events in silodosin-treated patients, 110 — 82% — were reported as "orgasm with absence of seminal emission." Retrograde flow and absent emission are different physiological events with different implications: one deposits semen in the bladder, the other means the seminal tract never contracts. The label term survives because it is the coded adverse-event category, and the distinction only appeared when someone went back to the case reports. It matters to a patient being counselled, and it matters to anyone reasoning about the mechanism.
Written into the record, not signed off as a reviewed claim
The men who lost emission had 1.75 times the odds of a symptomatic response
In plain words
The side effect turns out to track the benefit. Men who stopped producing semen were significantly more likely to reach a meaningful improvement in both their symptom score and their flow rate.
What was measured
Odds ratio for achieving a 3-point symptom-score and 3 mL/sec peak-flow improvement, with versus without absent seminal emission
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
In the same analysis of the two phase 3 trials, silodosin-treated patients with and without the ejaculatory effect both improved significantly against placebo on symptom score, peak flow and quality of life (P<0.02). The men who lost emission improved numerically more, though not significantly on the continuous measures (P>0.05). The responder analysis was significant: for patients with absent emission, the odds of achieving both a 3-point improvement in symptom score and a 3 mL/sec improvement in peak flow by study end were 1.75 times those of patients without it, P=0.0127. The authors concluded that absence of seminal emission may predict superior efficacy in individual patients. Read carefully, this is target-engagement evidence: the adverse effect is a biomarker for how thoroughly the alpha-1A receptor is blocked, and blockade produces both outcomes. It does not license a claim that the side effect should be sought.
Written into the record, not signed off as a reviewed claim
The stone trial missed its primary endpoint and reported a subgroup instead
In plain words
A randomised trial tested silodosin against placebo for passing kidney stones. Overall, 52% passed on the drug and 44% on placebo, p=0.2 — no difference. The result that got reported was a subgroup the trial was not sized to test.
What was measured
Spontaneous stone passage rate for all stones, silodosin versus placebo, with the distal subgroup reported separately
Effect estimate
No reviewed effect estimate exists for this record.
Limits
This entry records a failure.
From the source
Sur and colleagues ran a multi-institutional, randomised, double-blinded, placebo-controlled trial in adults with a unilateral ureteral calculus of 4 to 10 mm, randomised 1:1 to silodosin 8 mg or placebo for up to four weeks, with spontaneous stone passage as the primary outcome. The passage rate for all stones was 52% against 44%, p=0.2 — not significant. No significant differences were found for emergency-room visits, hospital admission or analgesic use either. Distal ureteric stones passed significantly more often on silodosin, p=0.01, and that is the finding the paper is usually cited for. The abstract itself states two limitations plainly: the intent-to-treat population was slightly below the calculated sample size, 232 against 240, and "sample sizes were not calculated for subgroup analyses." A subgroup result from a trial that missed its primary endpoint and was slightly underpowered for the endpoint it did specify is a hypothesis, and the authors say as much when they call for additional future studies.
Written into the record, not signed off as a reviewed claim
About 2.9 points of symptom score and 1.0 to 1.4 mL/sec of flow over placebo
In plain words
Both registration trials found a real effect. The symptom score fell about three points more than placebo, and the flow rate improved by about one millilitre a second more.
What was measured
Change in International Prostate Symptom Score total and peak urine flow rate at 12 weeks against placebo, in two registration trials
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
The label reports two 12-week placebo-controlled studies. International Prostate Symptom Score total fell 6.5 and 6.3 points against 3.6 and 3.4 on placebo, treatment effects of 2.9 points in both. Peak urine flow rose 2.2 to 2.9 mL/sec against 1.2 to 1.9 on placebo. The symptom-score margin is at the upper end of the alpha-blocker class — alfuzosin's three trials delivered about 2.0 points and tamsulosin's two delivered 2.8 and 1.5 — and it sits near the commonly cited minimally important difference of around three points for this instrument. That is worth stating precisely because it is unusual: most drugs in this file deliver margins that fall below their instrument's own threshold for a noticeable change, and this one lands close to it.
Source
US prescribing information for silodosin capsules, Clinical Studies section (openFDA drug label endpoint)
Role in the trial
Not matched to a registered study
Identity check
no open identity hold
Audit mark
verified
Review state
Written into the record, not signed off as a reviewed claim
A dedicated QT study in 189 men found no increase at all
In plain words
At three times the usual dose for five days, silodosin did not lengthen the heart's electrical interval at any measured time point. The antibiotic used as a positive control in the same study did.
What was measured
Individual corrected QT interval change at 8 mg and 24 mg for five days, against a moxifloxacin positive control
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
A cardiac safety trial in 189 healthy males aged 18 to 45 tested silodosin at 8 mg and 24 mg daily for five days. The label states silodosin "was not associated with an increase in individual corrected (QTcI) QT interval at any time during steady state measurement," while moxifloxacin as active control produced a maximum increase of 9.59 msec. That is a genuine negative with a demonstrably sensitive assay — the positive control worked. It is recorded here rather than omitted because a clean negative reported with its positive control is a different object from silence, and because tolterodine's label in this same file reports 11.84 msec at twice its therapeutic dose with confidence intervals overlapping the same comparator.
Source
US prescribing information for silodosin capsules, Clinical Pharmacology section (openFDA drug label endpoint)
Role in the trial
Not matched to a registered study
Identity check
no open identity hold
Audit mark
verified
Review state
Written into the record, not signed off as a reviewed claim
Four absolute contraindications, two of them about how the drug leaves the body
In plain words
Silodosin must not be taken by anyone with severe kidney impairment, severe liver impairment, or on a strong inhibitor of the enzyme that clears it. These are contraindications, not cautions.
What was measured
Contraindicated conditions and interactions listed on the US label, with the clearance basis for each
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
The US label lists four contraindications: severe renal impairment with creatinine clearance below 30 mL/min, severe hepatic impairment at Child-Pugh 10 or above, concomitant use of strong CYP3A4 inhibitors, and hypersensitivity. Two of those are clearance statements: the drug depends on CYP3A4 for metabolism and on the kidney for elimination of its metabolites, and removing either route raises exposure of a compound whose whole design point is high receptor occupancy. Alfuzosin's label carries a comparable CYP3A4 contraindication for the same structural reason. Tamsulosin, cleared by two enzymes rather than one, handles the same interaction with a warning.
Source
US prescribing information for silodosin capsules, Contraindications section (openFDA drug label endpoint)
Role in the trial
Not matched to a registered study
Identity check
no open identity hold
Audit mark
caution
Review state
Written into the record, not signed off as a reviewed claim
How many documents were read
17 documents were read for this substance.
RNAWiki source record
17 of them state the same halfLife, and they agree.
RNAWiki source record
17 of them state the same bioavailability, and they agree.
RNAWiki source record
17 of them state the same volumeOfDistribution, and they agree.
RNAWiki source record
Where else this substance is registered
FDA substance identifier (UNII)
CUZ39LUY82
RxNorm concept
809477
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What is missing or unclear◇Read from sources, not yet reviewed
How this medicine reached us
Kept near the foot of the page. A historical event moves up only when it changes something about this substance today.
What the approval register records
14 approved applications cover products containing this substance. The earliest was NDA022206, approved 20081008 to ABBVIE.
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7 questions this page could not answer
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Written for a clinical reader, and about the medicine as a whole rather than about one indication, population and set of trials. RNAWiki does not treat it as a programme conclusion and no reviewer has signed it off in that form. It is here word for word because it is what the record holds.
The most alpha-1A-selective alpha-blocker licensed, which lowered the International Prostate Symptom Score by 6.5 and 6.3 points against 3.6 and 3.4 on placebo in its two registration trials while producing absent or retrograde ejaculation in 28.1% of patients against 0.9% on placebo — the same receptor preference generating both results, and the trial that examined it finding that the men who lost seminal emission had 1.75 times the odds of a symptomatic response.
Recorded evidence blocks (10)
Q1
On the Silodosin label: indicated for what?
"1 INDICATIONS & USAGE Silodosin, a selective alpha-1 adrenergic receptor antagonist, is indicated for the treatment of the signs and symptoms of benign prostatic hyperplasia (BPH) [ see CLINICAL STUDIES ( 14 )]. Silodosin is not indicated for the treatment of hypertension.": indications and usage on Silodosin's label. DailyMed label · afbf4823-8663-4152-9346-ca42c7b7d722 · 2026-07-07
Q2
40 registered trials of Silodosin — at which phases?
Registered studies posting no result
33 of 40
40 registered studies of Silodosin: 16 phase4, 10 phase3, 8 phase2, 3 na, 2 phase1, 1 early phase1, 1 na or unstated. CLINICALTRIALS_SNAPSHOT · 2026-09-01
86 with a PubMed record
Show the evidence
phase4
16
phase3
10
phase2
8
na
3
phase1
2
early phase1
1
7 more recorded rows
na or unstated
1
completed
28
unknown
4
not yet recruiting
3
recruiting
2
terminated
2
withdrawn
1
recorded 2026-09-01 · last checked 2026-09-04
Q3
3 of Silodosin's trials stopped: accrual/recruitment, other?
"accrual of subjects did not occur as anticipated"; 3 of 40 registered studies
Show the evidence
Trial
NCT01560091
withdrawn; "accrual of subjects did not occur as anticipated"
NCT02090439
terminated; "Following difficulties in patient recruitment, we were forced to stop the study prematurely."
NCT02369744
terminated; "due to lack of suitable patient population"
recorded 2026-09-01 · last checked 2026-09-04
Q4
Human studies of Silodosin used Silodosin 8 mg — over how long?
Human studies of Silodosin used "Silodosin 8 mg". ClinicalTrials.gov · 2026-09-01
4 recorded entries; human; capsule; also "Silodosin 4 mg", "silodosin 8 mg capsule and the pyridostigmine bromide 60 mg tablet", "silodosin 8 mg capsule"
Show the evidence
human
NCT00740779
Silodosin 8 mg
NCT00740779
Silodosin 4 mg
NCT06319469
capsule; silodosin 8 mg capsule and the pyridostigmine bromide 60 mg tablet
NCT06319469
capsule; silodosin 8 mg capsule
recorded 2026-09-01 · last checked 2026-09-04
Q5
Silodosin's half-life is 24 hours — which schedules were studied?
24 hours, the half-life Silodosin's label states: "KMD-3213G, which has been shown in vitro to be active, has an extended half-life (approximately 24 hours) and reaches plasma exposure (AUC) approximately four times greater than that of silodosin." DailyMed label · afbf4823-8663-4152-9346-ca42c7b7d722 · 2026-07-07
bioavailability 32 %.
Show the evidence
half lifepharmacokinetics
24 hours; KMD-3213G, which has been shown in vitro to be active, has an extended half-life (approximately 24 hours) and reaches plasma exposure (AUC) approximately four times greater than that of silodosin.
bioavailabilitypharmacokinetics
32 %; Table 3 Mean (±SD) Steady State Pharmacokinetic Parameters in Healthy Males Following Silodosin 8 mg Once Daily with Food Cmax (ng/mL) t max (hours) t 1/2 (hours) AUC ss (ng•hr/mL) 61.6 ± 27.54 2.6 ± 0.90 13.3 ± 8.07 373.4 ± 164.94 C max = maximum concentration, t max = time to reach C max , t 1/2 = elimination half-life, AUCss = steady state area under the concentration-time curve Figure 1 Mean…
metabolismpharmacokinetics
Elimination Metabolism Silodosin undergoes extensive metabolism through glucuronidation, alcohol and aldehyde dehydrogenase, and cytochrome P450 3A4 (CYP3A4) pathways.
recorded 2026-07-07 · last checked 2026-09-04
Q6
Which 18 trials of Silodosin posted no result?
Posted no result
18 of 18 completed trials
Registrations
NCT00359905, NCT01259531, NCT01260129, NCT01228370, NCT01533389 and NCT01757769, and 12 more
Completion dates
oldest 2008-01; newest 2024-08-15
Show the evidence
Trial
NCT00359905
2008-01
NCT01259531
2011-09
NCT01260129
2011-10
NCT01228370
2012-01
NCT01533389
2012-08
NCT01757769
2013-08
12 further recorded trials
NCT02106182
2016-08-01
NCT06282731
2017-04-27
NCT04107896
2018-08-31
NCT05789732
2022-08-30
NCT05790902
2023-02-28
NCT05823662
2023-03-02
NCT02220829
2023-08
NCT05921370
2023-09-01
NCT06381206
2023-10-25
NCT06319469
2024-01-30
NCT07134907
2024-07-09
NCT06999135
2024-08-15
Q7
At the median, Silodosin's trials enrolled 140 people — anything larger?
Median enrolment
140
Largest enrolment
1228
Registered trials counted
40
Q8
What do 227 spontaneous reports say about Silodosin — and not say?
These are reports people sent to a regulator. They do not show the medicine caused the reaction. Nobody counted how many people took the medicine and reported nothing. The same event can be reported more than once, and many reports are incomplete. News coverage, lawsuits and new warnings change how often people report. A count is not a rate and not a risk.
Silodosin appears in spontaneous reports to regulators. Across the 10 most-reported reaction terms, 227 reaction mentions were counted: acute kidney injury 35; fall 32; loss of consciousness 30; confusional state 26. FAERS via Open Targets · CHEMBL24778 · 2026-06-24
Show the evidence
acute kidney injury
35
fall
32
loss of consciousness
30
confusional state
26
orthostatic hypotension
26
hyponatraemia
21
4 more recorded rows
syncope
20
urinary retention
13
atrioventricular block complete
12
granulomatous rosacea
12
recorded 2026-06-24 · last checked 2026-09-04
Q9
Which 10 reactions does Silodosin's label not list?
( 5.5 , 7.5 ) 7.1 Moderate and Strong CYP3A4 Inhibitors In a clinical metabolic inhibition study, a 3.8-fold increase in silodosin maximum plasma concentrations and 3.2-fold increase in silodosin exposure were observed with concurrent administration of a strong CYP3A4 inhibitor, 400 mg ketoconazole.
drug_interactions
Use of strong CYP3A4 inhibitors such as itraconazole or ritonavir may cause plasma concentrations of silodosin to increase.
drug_interactions
Concomitant administration of strong CYP3A4 inhibitors and silodosin is contraindicated [ see CONTRAINDICATIONS ( 4 ), WARNINGS AND PRECAUTIONS ( 5.4 ) and CLINICAL PHARMACOLOGY ( 12.3 ) ].
drug_interactions
The effect of moderate CYP3A4 inhibitors on the pharmacokinetics of silodosin has not been evaluated.
drug_interactions
Concomitant administration with moderate CYP3A4 inhibitors (e.g., diltiazem, erythromycin, verapamil) may increase concentration of silodosin.
2 more recorded rows
Interaction statementdrug_interactions
Exercise caution and monitor patients for adverse events when co-administering silodosin with moderate CYP3A4 inhibitors.
Interaction statementdrug_interactions
7.2 Strong P-glycoprotein (P-gp) Inhibitors In vitro studies indicated that silodosin is a P-gp substrate.
ChEMBL 37 — CC BY-SA 3.0 Unported · ChEMBL ATC CC BY-SA · ClinicalTrials.gov — US Government work · Open Targets 26.06 — CC0 · mixed register set; per-register licences in docs/specs/corpus-20k-sources.md · openFDA / DailyMed — US Government work
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