This page shows what was measured, who it was measured in, and what that does not settle.
What Clenbuterol does in the body
A horse asthma medicine taken without approval for fat loss.
Adrenaline works through several receptor subtypes. Clenbuterol selectively switches on the beta-2 subtype, which relaxes airways, releases fat from fat cells, and — over weeks — makes skeletal muscle fibres bigger. Unlike salbutamol it stays bound for a long time, so a single dose acts for many hours and it accumulates in tissue. That last property is why it was used illegally to make cattle leaner and heavier, and why the residue survives into the liver and meat of the animal. The same receptor is present on heart muscle, so the effects people report — pounding heart, tremor, low potassium — are not side effects in the sense of being off-target. They are the target, in another organ.
What happened in people
The only controlled human study found more lean mass but worse endurance.
✓ Reviewed first-read answer
Where this came from
A person wrote this and a reviewer approved it against this exact record. It carries no effect size.
A reviewer approved this against this record. The reviewed-claim record carrying the exact population and effect size does not exist yet.
No source is stored against this line.
The limit that matters most
No controlled human study has tested fat loss at the doses people use.
Where it acts
Beta-2 adrenergic receptors on bronchial smooth muscle, skeletal muscle fibres, adipocytes and cardiac myocytes
Kind of result
Measured performance
Supervision
RNAWiki has not recorded a supervision or regulatory status for this substance.
What the registries record it as
Its recorded molecular formula is C12H18Cl2N2O, weighing 277.19.
PubChem record · 2783 · read 2026-08-29
Where each sentence above came from
No recorded sentence describes the change this makes in a way that stands on its own. The page opens with what it is taken for instead, and the recorded explanation follows below.
Shown as the opening line on this page.
The limit a reviewer approved as the one that matters most here.
The four opening statements run to 138 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.
Stand-in result
A stand-in result is a number measured because the real result takes too long.
A picture of it, and where the picture fails
It is like judging a journey by the speedometer rather than by arriving.
Where that stops being true. Speed does predict arrival. Many stand-in results do not predict the real one.
What people get wrong. A stand-in result is often reported as the result itself.
A surrogate endpoint substituted for a clinical endpoint, valid only where the substitution has been shown to hold.
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.
Receptor
A receptor is a part of a cell that a signal fits into.
A picture of it, and where the picture fails
A receptor is like a lock waiting for one key.
Where that stops being true. A lock either opens or does not. A receptor can be half-triggered, or worn out.
What people get wrong. Fitting a receptor is read as causing a benefit. It causes a step, and nothing more.
A protein that binds a specific ligand and converts that binding into a cellular response.
Pathway
A pathway is a chain of steps inside a cell, each one setting off the next.
A picture of it, and where the picture fails
A pathway is like a row of dominoes.
Where that stops being true. Dominoes fall one way. Pathways loop back and can switch themselves off.
What people get wrong. Changing one step is read as changing the outcome. Other steps often absorb it.
An ordered series of molecular interactions producing a defined cellular change.
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.
Skeletal muscle function, cardiac function and exercise capacity, with body composition
✗ The study did not show it
Who was studied
Kamalakkannan 2008 randomised trial in chronic heart failure
How many people
0
Study design
Small randomised controlled trial
Compared against
Not recorded for this study
Kind of result
What a body can do day to day
What was found
Significant increase in lean mass and lean-to-fat ratio; maximal strength rose 27% on clenbuterol and 14% on placebo; endurance and exercise duration decreased after clenbuterol
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. An accompanying editorial in the same journal argued the trial showed impaired muscle quality and characterised the compound as potentially dangerous.
How far it carries. This study is recorded from the curated record, not from the registry match.
Form and route. Oral tablet (20 micrograms where licensed for humans), oral syrup (veterinary), unlicensed liquids
Interval reported. Not recorded in this summary
Written into the record, not signed off as a reviewed claim.
Salleras L et al. Epidemiologic study of an outbreak of clenbuterol poisoning in Catalonia, Spain. Public Health Rep 1995;110:338-342 (7610227) · a recorded source, not a stored snapshot
Prevalence and concentration of clenbuterol in athlete urine and in meat sampled from team hotels
✓ The study showed what it set out to show
Who was studied
FIFA U-17 World Cup 2011 food contamination investigation
How many people
208
Study design
Observational analytical investigation, doping control and food samples
Compared against
Not recorded for this study
Kind of result
A number that stands in for health
What was found
109 of 208 urine samples (52%) positive at 1-1,556 pg/mL; 14 of 47 meat samples (30%) positive at 0.06-11 ug/kg; 19 of 24 teams had at least one positive sample
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. No limitation is recorded for this study.
How far it carries. This study is recorded from the curated record, not from the registry match.
Form and route. Oral tablet (20 micrograms where licensed for humans), oral syrup (veterinary), unlicensed liquids
Interval reported. Not recorded in this summary
Written into the record, not signed off as a reviewed claim.
Salleras L et al. Epidemiologic study of an outbreak of clenbuterol poisoning in Catalonia, Spain. Public Health Rep 1995;110:338-342 (7610227) · a recorded source, not a stored snapshot
Salleras L et al. Epidemiologic study of an outbreak of clenbuterol poisoning in Catalonia, Spain. Public Health Rep 1995;110:338-342 (7610227) · a recorded source, not a stored snapshot
Salleras L et al. Epidemiologic study of an outbreak of clenbuterol poisoning in Catalonia, Spain. Public Health Rep 1995;110:338-342 (7610227) · a recorded source, not a stored snapshot
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 happened in people◇Read from sources, not yet reviewed
How close this is to real life
The top step is something a person would feel or care about. The bottom is a guess from software. Filled steps are where evidence exists for this substance.
□Living longer, or avoiding a major eventNo evidence recorded. Death, a heart attack, a stroke, a hospital stay.0 registered measures of this kind. 1 written-up study measured this and did not show a benefit.
■What a body can do day to dayEvidence recorded. Walking, dressing, breathing, recovering.1 registered measure of this kind.
■Measured performanceEvidence recorded. How much was lifted, how far was run, how fast.1 registered measure of this kind.
□Symptoms and quality of lifeNo evidence recorded. Pain, tiredness, mood, sleep, as the person rated it.No registered study measures this.
■A number that stands in for healthEvidence recorded. Cholesterol, blood sugar, bone density. A stand-in, not the thing itself.2 registered measures of this kind.
■A step measured inside a personEvidence recorded. Something measured in human tissue or human cells.A human record sits on the stored organism ladder.
■AnimalsEvidence recorded. Mice, rats, dogs. Useful for ideas, not proof about people.Stored records in Mouse, Rat. A result in animals says what to test next. It does not say what happens in people.
■Cells in a dishEvidence recorded. Cells or chemistry on a bench, far from a whole body.Stored mechanism abstracts describe steps measured in cells or tissue.
□A guess from softwareNo evidence recorded. Nobody measured it. RNAWiki never publishes one as a finding.RNAWiki stores no prediction for this record. Software can suggest a link. RNAWiki does not publish one as a finding.
Higher on these steps means closer to something a person would feel. It does not mean better done.
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
Clenbuterol
What a person takes: Oral tablet (20 micrograms where licensed for humans), oral syrup (veterinary), unlicensed liquids.
The measurement behind this step
Where licensed for people, a 20-microgram tablet. In the United States, a 72.5 microgram per millilitre veterinary syrup for horses. Outside both, unlicensed liquid preparations sold by dropper alongside SARMs and stimulants, where the label microgram figure has no analytical backing. The involuntary route — contaminated meat and adulterated heroin — accounts for the best-documented human exposures.
Getting in
Absorbed orally and cleared slowly
Taken as a tablet or a liquid, it is well absorbed and stays in the body far longer than an asthma inhaler drug.
╌╌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 bioavailability is high. The 3,5-dichloro-4-amino ring blocks the catechol-O-methyltransferase and sulfotransferase routes that clear salbutamol quickly, giving an elimination half-life on the order of a day and tissue accumulation on repeated dosing. That accumulation is what makes residues in animal liver and muscle a public health problem rather than an analytical curiosity.
Salleras L et al. Epidemiologic study of an outbreak of clenbuterol poisoning in Catalonia, Spain. Public Health Rep 1995;110:338-342 (7610227) · a recorded source, not a stored snapshot
Unlike a steroid, it does not need to get inside the cell — its target sits on the outside of the membrane.
──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
Beta-2 adrenergic receptors are G protein-coupled receptors on the plasma membrane of bronchial smooth muscle, adipocytes, skeletal myocytes and cardiac myocytes. No cellular entry is required; the drug binds the orthosteric pocket from the extracellular face.
Salleras L et al. Epidemiologic study of an outbreak of clenbuterol poisoning in Catalonia, Spain. Public Health Rep 1995;110:338-342 (7610227) · a recorded source, not a stored snapshot
Binding switches on a chain of signals inside the cell that ends with a rise in a universal messenger molecule.
╌╌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
Agonist binding couples the receptor to Gs, activating adenylyl cyclase and raising intracellular cyclic AMP, which activates protein kinase A. The slow off-rate of clenbuterol is why the signal is sustained where salbutamol is transient.
Salleras L et al. Epidemiologic study of an outbreak of clenbuterol poisoning in Catalonia, Spain. Public Health Rep 1995;110:338-342 (7610227) · a recorded source, not a stored snapshot
Different consequences in different tissues at the same time
Airways relax, fat cells release fat, muscle fibres grow, potassium moves into cells and the heart beats faster and harder.
──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
Protein kinase A relaxes bronchial smooth muscle, phosphorylates hormone-sensitive lipase to drive lipolysis, stimulates the sodium-potassium ATPase so serum potassium falls, promotes glycogenolysis and gluconeogenesis so glucose and lactate rise, and over weeks shifts skeletal muscle towards hypertrophy. In cardiac myocytes it raises rate and contractility. The measured poisoning picture — tachycardia, tremor, hypokalaemia, hyperglycaemia, raised lactate — is this list read in a single patient.
Salleras L et al. Epidemiologic study of an outbreak of clenbuterol poisoning in Catalonia, Spain. Public Health Rep 1995;110:338-342 (7610227) · a recorded source, not a stored snapshot
More lean mass, less endurance, and a cardiac cost
The body composition change is real. The functional gain is not, and six of thirteen confirmed poisoning cases had blood markers of heart muscle damage.
──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
In the randomised heart failure trial, lean mass and the lean-to-fat ratio rose while endurance and exercise duration fell. In the heroin adulteration outbreak, 6 of 13 confirmed exposures had biochemical evidence of myocardial injury. Chronic beta-adrenergic stimulation is a recognised driver of cardiac remodelling, and the human dose-response for that at fat-loss doses is not characterised.
Salleras L et al. Epidemiologic study of an outbreak of clenbuterol poisoning in Catalonia, Spain. Public Health Rep 1995;110:338-342 (7610227) · 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 it would be like to take◇Read from sources, not yet reviewed
Felt, measured, or meaningful
Three different things that get called the same word. Registered studies measured all three, and mixing them is how a blood test becomes a health claim.
Felt
Things a person could notice without a test.
No registered study measured anything of this kind.
Measured
Things only a test, a scale or a device shows.
heart rate
blood pressure
Meaningful
Things that change how a life goes, not only a number.
6 minute walk test
A registered study says what someone planned to measure. It does not say what they found. A number moving is not the same as a life going better. The two are shown apart here.
Felt, but not shown to help. A person notices a change. No study showed it leads anywhere good.
Measured, but not felt. A number moves. The person notices nothing. Both can be true.
Measured, but not shown to matter. A number moves in the good direction. Nobody showed that lives went better.
Matters, but takes years. The result that counts may take longer than anyone would keep watching.
Names that fit none of the three (4)
muscle hypertrophy
fiber cross sectional area
myonuclei
skeletal muscle proteome
These are harms, study-process measures, or names the rules did not recognise. They are shown rather than dropped.
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.
Veterinarians treating horses. Outside that, people using it for fat loss, often cycled in two-week blocks, and athletes who ingest it involuntarily from contaminated meat. It also turns up as an adulterant in illicit heroin.
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.
Where the result stopped carrying
Clenbuterol was never developed as a human anabolic or fat-loss agent; the human trials that exist studied bronchodilation and muscle wasting in cardiac patients
Its use as a livestock repartitioning agent was banned in the United States, the European Union and China after repeated human poisoning outbreaks traced to residues
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 for a different goal
The studies measured something else entirely.
On this record: Some registered studies measured things that match no goal on this page.
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 (10)
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
Not available
❝ 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 tablet (20 micrograms where licensed for humans), oral syrup (veterinary), unlicensed liquids
✎ 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
Where licensed for people, a 20-microgram tablet. 5 microgram per millilitre veterinary syrup for horses. Outside both, unlicensed liquid preparations sold by dropper alongside SARMs and stimulants, where the label microgram figure has no analytical backing. The involuntary route — contaminated meat and adulterated heroin — accounts for the best-documented human exposures.
✎ 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 and what that means for what is in the pack.
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
Documented human effects: tachycardia, tremor, palpitations, headache, nausea, chest pain, dyspnoea, hypokalaemia, hypophosphataemia, hyperglycaemia, raised lactate and biochemical myocardial injury. In the poison-centre series, 6 of 13 confirmed exposures had myocardial injury markers and beta-blockade was given in 10 without adverse effect. Food-borne exposures produced symptoms lasting 90 minutes to six days with no deaths in the reported outbreaks. Paediatric ingestions have been reported. There is no long-term human safety dataset at any dose used for fat loss.
Nobody counted how many people took this and were fine, so this cannot be turned into a rate.
Salleras L et al. Epidemiologic study of an outbreak of clenbuterol poisoning in Catalonia, Spain. Public Health Rep 1995;110:338-342 (7610227) · 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 tablet (20 micrograms where licensed for humans), oral syrup (veterinary), unlicensed liquids
✎ 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
5 microgram per millilitre veterinary syrup for horses. Outside both, unlicensed liquid preparations sold by dropper alongside SARMs and stimulants, where the label microgram figure has no analytical backing. The involuntary route — contaminated meat and adulterated heroin — accounts for the best-documented human exposures.
✎ 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 which forms are sold and how they compare.
No source is stored against this line.
What is recorded as being sold
2 products list this as an active ingredient in the United States drug directory. 2 of them contain it and nothing else.
FDA National Drug Code directory · 66583-0515 · read 2026-08-29
They are sold as powder.
FDA National Drug Code directory · 66583-0515 · read 2026-08-29
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 Clenbuterol 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 clenbuterol produces meaningful fat loss in healthy humans, which no randomised trial has measured at the doses used
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 an increase in lean mass means an increase in what the muscle can do, which the one trial measuring both contradicted
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 a positive doping test for clenbuterol identifies deliberate use, when half the samples at one tournament were positive from food
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 because it is a licensed bronchodilator somewhere, it has a characterised safety profile at fat-loss doses; the licensed human dose is 20 micrograms
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.
How much did people take in the studies?
The sources RNAWiki checked hold nothing for this field.
Why it matters. A result belongs to an amount. Without the amount the result floats free.
What would answer it
A stored source that records 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.
How fast does the body clear it?
The sources RNAWiki checked hold nothing for this field.
Why it matters. Without this, nothing on this page can say how long anything lasts.
What would answer it
A stored source that records 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 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 Clenbuterol 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.
Contaminated meat put clenbuterol in half the urine samples at a World Cup
In plain words
After five Mexican players tested positive, FIFA tested 208 doping samples and 47 meat samples during the 2011 U-17 World Cup. Clenbuterol was in 52% of the urine samples and 30% of the meat.
What was measured
Proportion of doping control urine samples and of hotel meat samples containing clenbuterol, with concentration ranges
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
Thevis et al. reported the investigation triggered by five adverse analytical findings for clenbuterol in the Mexican national team in out-of-competition controls in May 2011. During the FIFA U-17 World Cup in Mexico, 208 regular doping control samples were analysed by highly sensitive mass spectrometry and 47 meat samples were collected from team hotels and sent to RIKILT. Clenbuterol was detected in 14 of 47 meat samples (30%) at 0.06 to 11 micrograms per kilogram. Clenbuterol was found in 109 of 208 urine samples (52%) at 1 to 1,556 picograms per millilitre. Only 5 of 24 teams provided samples entirely free of it, and at least one of those was reportedly on a strict no-meat diet because the contamination problem was already known. No player was sanctioned. This is the reference case for inadvertent doping from food.
Written into the record, not signed off as a reviewed claim
It poisons people who eat contaminated liver
In plain words
Outbreaks in Spain and Italy hospitalised people hours after a meal, with tremor, palpitations, headache, low potassium and high blood sugar lasting days.
What was measured
Case counts, symptom frequencies, incubation and duration, and urinary clenbuterol concentrations in food-borne outbreaks
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
Salleras et al. investigated 113 cases of clenbuterol poisoning in Catalonia in 1992. More than half had nervousness, tachycardia, muscle tremors, myalgia and headache. Incubation ranged from 15 minutes to 6 hours and symptoms lasted 90 minutes to 6 days. Clenbuterol was detected in 47 urine samples at 11 to 486 parts per billion, with none detectable in serum. The association between eating veal liver and falling ill was significant at P < 0.0001. No deaths occurred. Brambilla et al. described a separate Italian outbreak of 15 people after eating meat, with nine hospitalised: distal tremor, palpitations, headache, tachypnoea and dyspnoea, moderate hyperglycaemia, hypokalaemia and leucocytosis beginning 0.5-3 hours after the meal and resolving over 3-5 days. Mean urinary clenbuterol was 28 ng/mL at 36 hours, from meat containing 1,140-1,480 ng/g. The first report of the phenomenon was a 1990 Lancet letter on illicit beta-agonist in liver.
Written into the record, not signed off as a reviewed claim
Documented cardiac injury in the heroin adulteration outbreak
In plain words
When clenbuterol was used to cut heroin along the US East Coast, 34 people presented to emergency departments and six had laboratory evidence of heart muscle injury.
What was measured
Blood and urine clenbuterol concentrations, electrolyte and lactate abnormalities, and biochemical myocardial injury in 13 confirmed exposures
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
Hoffman et al. reported an outbreak of clenbuterol-adulterated heroin identified across five US states over six months through poison-centre collaboration. Thirty-four probable or confirmed emergency department presentations were identified; 13 met criteria for confirmed exposure and clenbuterol was found in blood or urine in 12 of those 13, at 2.4-26 ng/mL in blood and 9.4-12,526 ng/mL in urine. Symptoms were nausea, chest pain, palpitations, dyspnoea and tremor. Findings included significant tachycardia, hypotension, hyperglycaemia, hypokalaemia and raised lactate. Six patients had biochemical evidence of myocardial injury. Ten received beta-adrenergic antagonists without adverse effect. An earlier single-case report documented prolonged tachycardia with hypokalaemia and hypophosphataemia confirmed by quantitative levels. Case reports of clenbuterol cardiac toxicity and of paediatric poisoning have continued since.
Written into the record, not signed off as a reviewed claim
It added lean mass and made endurance worse
In plain words
In the one randomised trial in patients, clenbuterol increased lean mass and the lean-to-fat ratio, and endurance and exercise duration went down rather than up.
What was measured
That a beta-2 agonist which increases lean mass improves functional capacity, when the randomised measurement showed endurance and exercise duration falling
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
Kamalakkannan et al. ran a small randomised controlled study of clenbuterol in patients with chronic heart failure, measuring skeletal muscle function, cardiac function and exercise capacity. Clenbuterol was well tolerated and produced a significant increase in both lean mass and the lean-to-fat ratio. Maximal strength increased significantly in both arms — 27% on clenbuterol and 14% on placebo. Endurance and exercise duration decreased after clenbuterol. An accompanying commentary in the same journal was titled "Clenbuterol impairs muscle quality and is potentially dangerous". The compound raises the amount of muscle and, on this measurement, lowers what the muscle can sustain. That dissociation is the same one seen with the SARMs, arrived at from a completely different receptor.
Written into the record, not signed off as a reviewed claim
The human fat-loss claim has no controlled trial
In plain words
The reason most people take clenbuterol — losing body fat — has never been tested in a randomised human trial at the doses used.
What was measured
That clenbuterol produces meaningful fat loss in humans at the doses used outside medicine, which no randomised trial has measured
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
The lipolytic and thermogenic argument rests on beta-2 receptor pharmacology and on livestock repartitioning studies, where clenbuterol was given to cattle, pigs and sheep to shift carcass composition towards lean tissue. In humans, the trials that exist studied bronchodilation, or muscle mass in patients with heart failure and left ventricular assist devices. None was designed to measure fat loss in healthy people, none used the intermittent high-dose regimens used outside medicine, and none ran long enough to describe what repeated cycles do. Recent reviews of beta-2 adrenergic agonism as an anti-obesity target treat the human question as open rather than answered.
Written into the record, not signed off as a reviewed claim
In the United States it is approved for one species, and it is not a horse owner
In plain words
The only US approval is an oral syrup for horses with airway obstruction. There is no approved human product, and using it in food animals is illegal.
What was measured
Approved species, indication and treatment duration limit in the United States veterinary regulation
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
21 CFR 520.452 provides for clenbuterol syrup at 72.5 micrograms of clenbuterol hydrochloride per millilitre, indicated for the management of horses affected with airway obstruction such as occurs in chronic obstructive pulmonary disease, with a 30-day treatment limit and a stepwise dose escalation to identify non-responders. Nothing in the United States authorises human use. Use as a growth promoter in food-producing animals is prohibited in the United States, the European Union and China, and the residue surveillance programmes that exist in all three are a direct consequence of the poisoning outbreaks. Several other countries license 20-microgram human bronchodilator tablets, which is why the compound is straightforwardly obtainable and why its legal status differs completely depending on where the reader is standing.
Source
21 CFR 520.452, Clenbuterol syrup — specifications, sponsor and conditions of use; European and Chinese prohibitions on beta-agonist growth promoters
Role in the trial
Not matched to a registered study
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The earliest marketing start date recorded for a listed product is 20160614.
FDA National Drug Code directory · 66583-0515 · read 2026-08-29
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A long-acting beta-2 agonist that increases lean mass and decreases endurance in the one randomised human trial that measured both, poisons people who eat contaminated liver, and produced clenbuterol in 52% of 208 doping control samples at a football tournament in a country where 30% of the meat sampled was contaminated.
Recorded evidence blocks (11)
Q1
What did Clenbuterol's largest trial (90 people) and its longest (3.7 years) measure?
90 people in Clenbuterol's largest registered study, 3.7 years in its longest registered window, measuring Percent of Subjects Who Experience LVAD Removal and Subsequent Freedom From Mechanical Circulatory Support or Heart Transplantation for 1-year After Explantation. ClinicalTrials.gov · 2026-09-01
6 phase2, 3 phase1, 2 na; NCT06169046; 2027-12-31; no ageing endpoint recorded. Last human test completed 2024, NCT04921306.
Interpretation These counts include studies where Clenbuterol was a comparison treatment, a background treatment or an exposure in an observational study, and the longest window may be a planned end date. Trial roles have not yet been classified for this record.
Show the evidence
phase2
6
phase1
3
na
2
Last recorded human testNCT04921306
2024-03-01
recorded 2026-09-01 · last checked 2026-09-04
Q2
From mouse to human: where has Clenbuterol shown lifespan?
Percent of Subjects Who Experience LVAD Removal and Subsequent Freedom From Mechanical Circulatory Support or Heart Transplantation for 1-year After… — the recorded outcome words.
Show the evidence
mouse
healthspan
rat
lifespan
humanNCT00585546
mechanism-only; Percent of Subjects Who Experience LVAD Removal and Subsequent Freedom From Mechanical Circulatory Support or Heart Transplantation for 1-year After Explantation; 10
recorded 2026-09-01 · last checked 2026-09-04
Q3
2 of Clenbuterol's trials stopped: funding/business, other?
6-minute-walk test; Frequency of Clenbuterol-related adverse reactions; latest 2028-07
Show the evidence
Trial
NCT06169046
"A Placebo-controlled Study of Clenbuterol in Spinal and Bulbar Muscular Atrophy"; n 90; "6-minute-walk test"; 2027-12-31
NCT06721299
"Clenbuterol to Target DUX4 in FSHD"; n 30; "Frequency of Clenbuterol-related adverse reactions"; 2028-07
recorded 2026-09-01 · last checked 2026-09-04
Q7
Which running trial of Clenbuterol could settle function?
NCT06169046 measures 6-minute-walk test, reading out 2027-12-31.
1 open trial; n 90; "A Placebo-controlled Study of Clenbuterol in Spinal and Bulbar Muscular Atrophy"
Show the evidence
TrialNCT06169046
"A Placebo-controlled Study of Clenbuterol in Spinal and Bulbar Muscular Atrophy"; n 90; "6-minute-walk test"; 2027-12-31
Q8
Which 2 trials of Clenbuterol posted no result?
Posted no result
2 of 2 completed trials
Registrations
NCT03800290 and NCT04921306
Completion dates
oldest 2021-04-23; newest 2024-03-01
Show the evidence
Trial
NCT03800290
2021-04-23
NCT04921306
2024-03-01
Q9
At the median, Clenbuterol's trials enrolled 21.5 people — anything larger?
Median enrolment
21.5
Largest enrolment
90
Registered trials counted
10
Q10
Was Clenbuterol studied with exercise?
exercise is named in Clenbuterol's label sentences: "In a small, randomized controlled study, we investigated the effect of clenbuterol on skeletal muscle function, cardiac function, and exercise capacity in patients with chronic heart failure." openfda-label+europepmc · 2008-04-01
1 recorded statement; exercise
Show the evidence
exercise
In a small, randomized controlled study, we investigated the effect of clenbuterol on skeletal muscle function, cardiac function, and exercise capacity in patients with chronic heart failure.
recorded 2008-04-01 · last checked 2026-09-04
Q11
What is recorded about Clenbuterol and mTOR?
"Herein, we examined the effect of clenbuterol ingestion on metabolic rate as well as skeletal muscle mammalian target of rapamycin (mTOR) phosphorylation and protein kinase A (PKA)-signaling in six young men." — where Clenbuterol and mTOR appear together. Europe PMC · pathway abstract search · 2020-01-19
"Herein, we examined the effect of clenbuterol ingestion on metabolic rate as well as skeletal muscle mammalian target of rapamycin (mTOR) phosphorylation and protein kinase A (PKA)-signaling in six young men."
PMID 27555230
"In contrast, clenbuterol, an mTOR activator, blunted the effect of rapamycin on serum creatinine (4 ± 0.6 vs 2.3 ± 0.3 mg/dL; P<.05), autophagy induction and p-mTOR expression."
autophagyPMID 27555230
"In contrast, clenbuterol, an mTOR activator, blunted the effect of rapamycin on serum creatinine (4 ± 0.6 vs 2.3 ± 0.3 mg/dL; P<.05), autophagy induction and p-mTOR expression."
mTORPMID 22300302
"Moreover, the calpastatin-induced inhibition of hypertrophy under clenbuterol treatment was not related to a decreased mTOR-dependent initiation of protein translation."
IGF-1
PMID 20577844
"Clenbuterol-treated cultures also showed elevated insulin-like growth factor I (IGF-1) mRNA and activation of the protein kinase Akt."
PMID 20577844
"Together these data show that clenbuterol acts to induce mild cardiac hypertrophy in cardiac myocytes via paracrine signalling involving fibroblast-derived IGF-1."
PMID 27017193
"Clenbuterol, a selective β2 receptor agonist, enhanced the CI-MPR expression in striated muscle through Igf-1 mediated muscle hypertrophy, which correlated with increased CI-MPR (also the Igf-2 receptor) expression."
AMPKPMID 18656451
"Finally, lipin-1 mRNA expression in rat triceps muscle was significantly elevated at 6h after subcutaneous injections of 5-aminoimidazole-4-carboxamide ribonucleoside (AICAR) or clenbuterol, which are 5'-AMP-activated protein kinase (AMPK) and beta2-adrenergic receptor (beta2-AR) activators, respectively."
recorded 2020-01-19 · last checked 2026-09-04
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