This page shows what was measured, who it was measured in, and what that does not settle.
What Isotonitazene does in the body
Nothing. These are 1950s analgesic candidates that were never developed, resurfacing sixty years later in the illicit drug supply because they are easy to make and are not on the lists
Nitazenes are selective agonists at the µ-opioid receptor — the same target as morphine and fentanyl — but built on an entirely different chemical scaffold, a benzimidazole rather than a piperidine or a morphinan. That structural difference is the whole reason they are in the drug supply: it puts them outside compound-specific drug laws and outside the mass-spectrometry libraries forensic laboratories were using. The pharmacology is otherwise ordinary opioid pharmacology, including the respiratory depression that kills, and naloxone reverses it. The problem is quantity: doses that matter are measured in micrograms, so the margin between a dose and a lethal dose is a matter of weighing accuracy.
What happened in people
Isotonitazene blood concentrations averaging 2.2 ± 2.1 ng/mL across 18 forensic cases, with two deaths at 0.4 ng/mL and no other opioid present
✎ 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.
That a single "times stronger than fentanyl" multiplier describes analgesic, respiratory-depressant and lethal potency alike
Where it acts
µ-opioid receptors in the brainstem respiratory centres — the site that determines whether an opioid overdose is fatal
Kind of result
A number that stands in for health
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 · ZFY1ZBQ8AV · 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.
A limit recorded against this substance. Not signed off as a reviewed claim.
The four opening statements run to 165 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.
Biomarker
A biomarker is a number from a test that stands in for something about health.
A picture of it, and where the picture fails
A biomarker is like a fuel gauge.
Where that stops being true. A gauge is wired to the tank. Many biomarkers are only loosely tied to health.
What people get wrong. A better number is read as a better life. Several medicines improved a number and helped nobody.
A measurable indicator used as a substitute for a clinical outcome of interest.
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.
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.
µ-opioid receptor binding affinity and activation potency for 15 nitazenes, with in vivo effects for 7
✓ The study showed what it set out to show
Who was studied
Vandeputte et al. 2024 pre-emptive characterisation of 15 nitazenes
How many people
15
Study design
In vitro pharmacology with in vivo mouse evaluation
Compared against
Not recorded for this study
Kind of result
A number that stands in for health
What was found
All 15 bound µ with nanomolar affinity; functional potency of several comparable to or exceeding fentanyl; α'-methyl etonitazene most potent across all functional assays
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. β-arrestin 2 recruitment is one measure of receptor activation and does not by itself predict respiratory-depressant potency in humans. Mouse data are subcutaneous and do not establish a human dose.
How far it carries. This study is recorded from the curated record, not from the registry match.
Form and route. Illicit powder, counterfeit tablets, and adulteration of other opioid products
Interval reported. Not recorded in this summary
Written into the record, not signed off as a reviewed claim.
Confirmation, quantitation and metabolite identification of isotonitazene in authentic casework
✓ The study showed what it set out to show
Who was studied
Krotulski et al. 2020 isotonitazene forensic case series
How many people
18
Study design
Forensic toxicology casework analysis
Compared against
Not recorded for this study
Kind of result
A number that stands in for health
What was found
Blood 2.2 ± 2.1 ng/mL (median 1.75, range 0.4-9.5); urine 2.4 ± 1.4 ng/mL; 9 of 18 previously negative for any opioid; 4 metabolites identified
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. Case ascertainment depended on a method that did not exist beforehand, so the series describes what became visible rather than what occurred. Postmortem redistribution is not accounted for.
How far it carries. This study is recorded from the curated record, not from the registry match.
Form and route. Illicit powder, counterfeit tablets, and adulteration of other opioid products
Interval reported. Not recorded in this summary
Written into the record, not signed off as a reviewed claim.
RNAWiki holds 3 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
Isotonitazene
What a person takes: Illicit powder, counterfeit tablets, and adulteration of other opioid products.
The measurement behind this step
There is no medical delivery system, because no member of this class has ever been a medicine. In practice the compound reaches a person inside something sold as heroin or as a pharmaceutical tablet, at microgram quantities distributed through a product nobody has assayed. The first indication of arrival in a population has repeatedly been a change in the toxicology rather than a change in the market.
Getting in
Arrives inside something else
Rarely sold under its own name. It turns up in counterfeit pills, in powder sold as heroin, and mixed with other synthetic opioids.
╌╌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
Microgram-range active doses mean a fraction of a milligram distributed unevenly through a tablet or a powder. Nine of 18 cases in the first US isotonitazene series had previously been reported negative for any opioid, which describes the distribution route as well as the analytical gap.
Lipophilic and small; it reaches the brain quickly by any route the user takes.
╌╌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
Rapid central distribution consistent with a lipophilic small molecule. Metabolism proceeds by N- and O-dealkylation and by nitro reduction, giving 5-amino-isotonitazene, which was found in most blood samples in the first case series.
The same receptor as morphine and fentanyl, reached by a completely different molecular shape.
╌╌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
Selective µ agonism with nanomolar binding affinity across all 15 compounds in the 2024 panel, with β-arrestin 2 recruitment potency comparable to or exceeding fentanyl for several. The 2-benzylbenzimidazole scaffold shares no structural relationship with morphinans or anilidopiperidines.
The brainstem stops responding to rising carbon dioxide, and breathing slows and then stops. This is how every opioid overdose kills.
╌╌Measured in animals. A result in animals says what to test next. It does not say what happens in people.
The measurement behind this step
µ-receptor-mediated depression of brainstem respiratory centres, the standard opioid mechanism. In mice, subcutaneous administration produced dose-dependent antinociception, locomotor change and hypothermia — the conventional opioid profile.
Reversible with naloxone, at concentrations of a few nanograms
Naloxone works, because it competes at the same receptor regardless of the drug's chemical family. The complication is that a very potent agonist may outlast one dose.
╌╌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
Competitive µ antagonism by naloxone applies to this class as to any other µ agonist. Fatal blood concentrations in the first isotonitazene series averaged 2.2 ± 2.1 ng/mL, with two deaths at 0.4 ng/mL and no other opioid present — the concentration scale on which reversal has to work.
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.
Almost nobody knowingly. In the first US forensic series of 18 isotonitazene-positive cases, nine had previously tested negative for any opioid — the compound was invisible to the panel being used.
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
None of the 2-benzylbenzimidazoles was ever developed into a medicine despite being invented as analgesic candidates
Compound-specific scheduling has been followed each time by a structurally adjacent analogue appearing in casework before it was listed
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
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
Illicit powder, counterfeit tablets, and adulteration of other opioid products
✎ 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
There is no medical delivery system, because no member of this class has ever been a medicine. In practice the compound reaches a person inside something sold as heroin or as a pharmaceutical tablet, at microgram quantities distributed through a product nobody has assayed. The first indication of arrival in a population has repeatedly been a change in the toxicology rather than a change in the market.
✎ 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
Not recorded.
∅ Nothing recorded
Where this came from
RNAWiki holds nothing here and says so rather than guessing.
No register entry is recorded.
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
The hazard is opioid respiratory depression at concentrations of a few nanograms per millilitre in blood. In the first US forensic series, average blood isotonitazene was 2.2 ng/mL and two fatal cases had 0.4 ng/mL with no other opioid detected. Because the compounds are selective µ agonists, naloxone reverses them; the practical concern is that a highly potent agonist may outlast a single dose, so repeated dosing or an infusion may be needed. Routine opioid immunoassays do not detect them and standard confirmation panels did not until the specific compounds were added, so a negative toxicology result does not exclude a nitazene. Co-detection with other synthetic opioids and with benzodiazepine-type compounds is common in casework.
Nobody counted how many people took this and were fine, so this cannot be turned into a rate.
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
Illicit powder, counterfeit tablets, and adulteration of other opioid products
✎ 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
In practice the compound reaches a person inside something sold as heroin or as a pharmaceutical tablet, at microgram quantities distributed through a product nobody has assayed. The first indication of arrival in a population has repeatedly been a change in the toxicology rather than a change in the market.
✎ 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
112464 marketed supplement labels list this ingredient, classed as botanical, botanical with nutrients and other combinations.
Those labels carry all other, nutrient and structure/function claims. A claim of that kind is written by the manufacturer and is not assessed by any regulator, so its presence says nothing about whether it is true.
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 Isotonitazene 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 a single "times stronger than fentanyl" multiplier describes analgesic, respiratory-depressant and lethal potency alike
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 scheduling a named nitazene reduces the class's presence in the supply; the observed response has been substitution
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 published case counts measure the burden of the class, when detection depends on a laboratory having already characterised the specific compound
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 1950s and 1960s animal analgesia literature provides human-equivalent potency figures
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 Isotonitazene 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.
All fifteen tested bound µ at nanomolar affinity; several matched or beat fentanyl
In plain words
Researchers synthesised fifteen nitazenes that had not yet appeared on the market and tested them. Every one bound the opioid receptor tightly, and several were as potent as fentanyl or more so.
What was measured
µ-opioid receptor binding affinity and β-arrestin 2 recruitment potency for 15 nitazenes against fentanyl, with in vivo effects for 7 in mice
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
Vandeputte et al. synthesised and characterised 15 structurally diverse nitazenes chosen as compounds that might be predicted to emerge. µ-opioid receptor affinity was measured by [3H]DAMGO competition binding in rat brain tissue, and activation by a cell-based β-arrestin 2 recruitment assay. All 15 bound µ with nanomolar affinities, and the functional potency of several was comparable to or exceeded that of fentanyl. Seven, including etonitazene, were also evaluated in male C57BL/6J mice after subcutaneous administration, showing dose-dependent antinociception, locomotor and body-temperature effects. Structure-activity findings included high opioid-like activity for methionitazene, iso-butonitazene, sec-butonitazene and two etonitazene analogues; the most potent across all functional assays was α'-methyl etonitazene. The design is the point: this is pre-emptive characterisation of compounds before they reach the market, which is the only way risk assessment can run ahead of a class that replaces itself.
Written into the record, not signed off as a reviewed claim
Fatal at 0.4 ng/mL, and invisible to the panel in half the cases
In plain words
In the first US forensic series, eighteen deaths involved isotonitazene at an average blood level of 2.2 nanograms per millilitre. Nine of those eighteen had already been reported as negative for any opioid.
What was measured
Isotonitazene concentrations in blood, urine and vitreous across 18 forensic cases, with metabolite identification
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
Krotulski et al. confirmed and quantified isotonitazene in blood, urine and vitreous fluid by LC-MS/MS with standard addition, and identified metabolites by LC-QTOF-MS. Eighteen cases were confirmed positive, nine of which had previously been negative for any opioid on the testing then in use. Average blood concentration was 2.2 ± 2.1 ng/mL (median 1.75, range 0.4 to 9.5); average urine concentration 2.4 ± 1.4 ng/mL (median 2.7, range 0.6 to 4.0). The lowest blood concentration, 0.4 ng/mL, occurred in two cases with no other opioid present, in death investigations. Four metabolites were detected in vivo: N- and O-dealkylation products were the most prominent urinary biomarkers and 5-amino-isotonitazene appeared in most blood samples. The authors conclude that toxicologists, medical examiners and coroners should add isotonitazene to testing procedures — which is to say that until they did, these deaths were being recorded as something else.
Written into the record, not signed off as a reviewed claim
Abandoned in the 1950s, back in the drug supply sixty years later
In plain words
CIBA invented these compounds as painkillers in the late 1950s and never developed any of them. They reappeared around 2019, unscheduled and easy to make, and one of them has been linked to at least 200 deaths.
What was measured
Historical development record against current illicit-market presence and attributed fatality count
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
Ujváry et al., writing with the European Monitoring Centre for Drugs and Drug Addiction, describe etonitazene and related 2-benzylbenzimidazoles as potent analgesics invented in CIBA's research laboratories in the late 1950s. Their structure is unrelated to poppy-derived and other synthetic analgesics, but they are selective µ-opioid agonists with morphine-like pharmacotoxicological properties in animals and humans. None was developed into a medicine; etonitazene and some derivatives were instead used as receptor probes and in animal addiction-behaviour studies. Several unscheduled members of this synthetically accessible class emerged on the illicit market from around 2019, and isotonitazene has been implicated in at least 200 fatalities in Europe and North America. The record here is the reversal: compounds that failed to become medicines, preserved in the pharmacology literature as research tools, becoming a public-health problem because that literature is a synthesis manual for anyone looking for an unlisted opioid.
Written into the record, not signed off as a reviewed claim
Scheduled compound by compound, replaced compound by compound
In plain words
DEA placed isotonitazene in Schedule I in August 2020. Metonitazene and others followed. Each listing has been followed by a different analogue appearing in casework.
What was measured
Scheduling dates against the dates of first forensic appearance for successive class members
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
DEA published a notice of intent to temporarily place isotonitazene in Schedule I on 18 June 2020 (85 FR 36819), with the temporary scheduling final order published 20 August 2020 (85 FR 51342). Isotonitazene, metonitazene and butonitazene now appear by name in 21 CFR part 1308. Forensic laboratories documented metonitazene in US casework in 2021 and N-pyrrolidino etonitazene (etonitazepyne) in 2022, each characterised pharmacologically and in case series after it had already appeared. The 2024 pre-emptive panel of 15 unlisted nitazenes was designed explicitly to get ahead of that cycle. This is the same replacement dynamic recorded on the synthetic cannabinoid page, with a sharper consequence: the substitutions here are opioids, and the relevant endpoint is respiratory arrest.
Source
DEA notice of intent 85 FR 36819 (18 June 2020) and final order 85 FR 51342 (20 August 2020); 21 CFR part 1308, current eCFR text; Vandeputte MM et al. Arch Toxicol 2022;96:1845-1863
Role in the trial
Not matched to a registered study
Identity check
no open identity hold
Audit mark
contested
Review state
Written into the record, not signed off as a reviewed claim
Ordinary opioid pharmacology on an unfamiliar scaffold
In plain words
Chemically these look nothing like morphine or fentanyl. Pharmacologically they behave the same way: selective at the µ receptor, morphine-like in animals and people, and reversible with naloxone.
What was measured
Receptor selectivity and in vivo opioid-like effect profile across the 2-benzylbenzimidazole class
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
The 2-benzylbenzimidazole core is structurally unrelated to the morphinan, phenylpiperidine and anilidopiperidine scaffolds of the established opioids, which is why the class evaded both scheduling and detection. The pharmacology is nonetheless conventional: selective µ-opioid receptor agonism with morphine-like pharmacotoxicological properties in animals and humans, dose-dependent antinociception, locomotor change and hypothermia in mice, and β-arrestin 2 recruitment at the same receptor. The practical consequence is that opioid overdose management applies: naloxone is a competitive µ antagonist and does not care about the scaffold. The caution that follows from potency is about duration and dose rather than mechanism — a highly potent agonist may outlast a single naloxone dose.
Written into the record, not signed off as a reviewed claim
Potency multiples relative to fentanyl are not a single number
In plain words
Statements like "twenty times stronger than fentanyl" appear constantly. The published measurements give potency in specific assays, and the ranking changes between assays and between species.
What was measured
That a single potency multiple relative to fentanyl describes a nitazene's analgesic, respiratory-depressant and lethal potency alike
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
The measured statement in the 2024 panel is that all 15 compounds bound µ with nanomolar affinity and that several had functional potency comparable to or exceeding fentanyl, in a β-arrestin 2 recruitment assay with fentanyl as the on-plate reference. That is an assay-specific ratio. It is not equivalent to a ratio of analgesic potency in humans, a ratio of respiratory-depressant potency, or a ratio of lethal dose, and the numbers do not transfer between those quantities or between in vitro and in vivo systems. Widely repeated multipliers usually originate in single animal analgesia assays from the 1950s and 1960s literature. The defensible public-health statement is that active doses are in the microgram range and that several class members are at least as potent as fentanyl — which is sufficient, and which this record states instead of a multiplier.
Written into the record, not signed off as a reviewed claim
The class arrives inside other drugs
In plain words
People are not seeking nitazenes. They appear in counterfeit tablets, in powders sold as heroin, and alongside other synthetic opioids — which is why the first sign of their arrival is usually a rise in deaths.
What was measured
Proportion of forensic cases positive for a nitazene that had previously been reported negative for any opioid
Effect estimate
No reviewed effect estimate exists for this record.
Limits
See the technical detail.
From the source
The forensic literature documents these compounds in casework rather than in seizures of material sold under its own name: isotonitazene appearing in cases previously negative for any opioid, metonitazene assessed in United States forensic toxicology casework in 2021, N-pyrrolidino etonitazene characterised alongside a case series in 2022. Nine of the 18 isotonitazene cases had been reported negative for opioids before the targeted method existed, which is the clearest available measure of how a compound of this class enters a population: undetected, inside a product sold as something else. This is filed as measured because it is a property of the case series, and it is the reason surveillance for this class depends on non-targeted acquisition and retrospective reprocessing rather than on adding one more analyte to a panel.
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What is not here
8 questions this page could not answer
These sections were prepared and left out because there was nothing to put in them. They are listed rather than hidden, so the gaps in this record are visible.
What was measured, goal by goal — found nothing in the sources checked.
How close this is to real life — found nothing in the sources checked.
Felt, measured, or meaningful — found nothing in the sources checked.
How long anything takes — found nothing in the sources checked.
What it may clash with — found nothing in the sources checked.
Other ways to the same goal — found nothing in the sources checked.
How this medicine reached us — found nothing in the sources checked.
What changed on this page — found nothing in the sources checked.
The record as stored
The full record, for auditing
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The older medicine-wide conclusion held in this record
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.
A class of analgesic candidates abandoned by CIBA in the late 1950s, now the fastest-moving part of the illicit opioid supply: all fifteen tested in a 2024 panel bound the µ-opioid receptor with nanomolar affinity, several matching or exceeding fentanyl, with isotonitazene implicated in at least 200 deaths across Europe and North America and fatal blood concentrations as low as 0.4 ng/mL.
Recorded evidence blocks (0)
Where it is registeredIdentifiers, relations and other names
Nitazenes (Isotonitazene and the 2-Benzylbenzimidazole Opioids)
Salt form
None. Never marketed as a medicine anywhere. Sold in the illicit supply as counterfeit tablets, in heroin substitutes and as powder
Also called
ISO (OPIOID RECEPTOR AGONIST), N,N-DIETHYL-2-((4-(1-METHYLETHOXY)PHENYL)METHYL)-5-NITRO-1H-BENZIMIDAZOLE-1-ETHANAMINE, N,N-DIETHYL-2-(2-(4 ISOPROPOXYBENZYL)-5-NITRO-1H-BENZIMIDAZOL-1-YL)ETHAN-1-AMINE, TONI
Component
Nitazenes (Isotonitazene and the 2-Benzylbenzimidazole Opioids)
✗ required summary fields resolved: 4 required field(s) not terminal: Why people use it, Best-supported result, Biggest unanswered question, Human evidence
✓ public claims reviewed: 0 reviewed claim(s); drafts are never rendered
✓ source coverage passed: 1 source rows
✓ no critical contamination: no quarantine open
✓ canonical metadata passed: slug and display name present
✓ no raw internal fields: enforced by the copy-contract test over the rendered page
This is a record of evidence. It is not medical advice, and it does not say this substance suits you. Nothing here says any substance on RNAWiki is appropriate for a child.