2-Methyl-AP-237 & AP-238: Complete Toxicology, Overdose, Dependence & Safety Monograph

2-Methyl-AP-237 & AP-238: Complete Toxicology, Overdose, Dependence & Safety Monograph

Emergency safety: 2-methyl-AP-237 and AP-238 are opioid agonists. If someone is difficult or impossible to wake, breathing slowly or irregularly, blue/gray around the lips, choking/gurgling while unresponsive, or has collapsed after an unknown opioid product, call emergency services and administer naloxone if available.

Quick answer

2-Methyl-AP-237 (often called “2MAP”) and AP-238 are synthetic opioids in the cinnamylpiperazine family.

They are chemically distinct from:

• fentanyl;
• nitazenes;
• U-47700;
• brorphine.

But they converge on the same clinically important target: the mu-opioid receptor (MOR).

Their history runs through bucinnazine/AP-237, a piperazine opioid synthesized in the late 1960s and used medically for chronic cancer pain in China. 2-Methyl-AP-237 is a methylated derivative within that chemical lineage. PMID 34528782

The modern harm-reduction issue is that related cinnamylpiperazines later entered unregulated NPS markets.

Human evidence now includes:

• multiple postmortem cases;
• direct fatal intoxication;
• a mixed 2-methyl-AP-237/AP-238 intoxication report;
• validated MOR activity;
• metabolism data;
• international and U.S. scheduling of 2-methyl-AP-237.

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Evidence at a glance

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Identity and names

2-Methyl-AP-237

Common names include:

• 2-methyl-AP-237;
• 2MAP;
• 2-methyl bucinnazine;
• methylated AP-237.

Class: cinnamylpiperazine synthetic opioid

AP-238

AP-238 is a distinct cinnamylpiperazine analogue.

It should not be treated as a synonym for 2-methyl-AP-237.

This is especially important when discussing:

• potency;
• toxic concentrations;
• metabolites;
• legal status.

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History: the bucinnazine lineage

Bucinnazine/AP-237 was synthesized in the late 1960s.

Unlike most modern RC opioids, bucinnazine itself has a history of medical use for cancer-associated pain in China. PMID 34528782

That history can create a misleading impression that newer derivatives are “pharmaceutical-like.”

They are not approved formulations.

2-Methyl-AP-237 and AP-238 entered a different environment:

• unregulated online markets;
• unknown manufacturing standards;
• uncertain dose uniformity;
• little human safety characterization.

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Why the cinnamylpiperazines emerged

After the United States and China adopted broad fentanyl-related controls, illicit markets began shifting toward non-fentanyl synthetic opioids with different chemical scaffolds.

The new waves included:

• nitazenes;
• brorphine;
• cinnamylpiperazines such as 2-methyl-AP-237 and AP-238.

A 2022 postmortem-surveillance study documented hundreds of cases involving these newer opioid classes after fentanyl core-structure scheduling. PMID 36103391

This is another example of chemical substitution rather than disappearance of opioid demand.

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Pharmacodynamics

Mu-opioid receptor activation

A 2022 study directly compared:

• 2-methyl-AP-237;
• AP-237;
• para-methyl-AP-237;
• AP-238.

All activated MOR in the experimental assay. PMID 35275255

Among the tested compounds:

• AP-238 was the most potent in that assay;
• 2-methyl-AP-237 showed the greatest efficacy;
• overall in-vitro MOR activation was lower than fentanyl and several other highly potent NSOs.

What that means clinically

Lower receptor potency than fentanyl does not mean safe.

Human overdose risk still depends on:

• amount;
• route;
• product concentration;
• tolerance;
• metabolism;
• co-drugs.

The study's fatal cases prove the family can produce lethal real-world opioid toxicity.

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Human postmortem evidence

The 2022 toxicology study included authentic cases received from February 2020 through April 2021.

2-Methyl-AP-237

Four postmortem cases had blood concentrations ranging from:

820–5800 ng/mL

AP-238

Two postmortem cases had concentrations of:

87 and 120 ng/mL

These values are useful for forensic context.

They are not safe/lethal cutoffs.

The much higher 2-methyl-AP-237 concentrations compared with ultra-potent nitazenes are consistent with its lower MOR potency in the tested assay.

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Direct fatal 2-methyl-AP-237 case

A 2023 case report described a 54-year-old man found deceased with a container labeled “2MAP.”

Advanced toxicology confirmed:

• 2-methyl-AP-237 in blood and urine;
• three hydroxylated metabolites;
• alprazolam in blood.

Measured 2-methyl-AP-237 concentrations were:

• 480 ng/mL in blood;
• 4200 ng/mL in urine. PMID 37264551

A field test of the powder had initially indicated fentanyl.

This is an excellent example of why field testing and product labels are not definitive chemical identification.

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Mixed 2-methyl-AP-237 + AP-238 intoxication

A 2023 Australian report documented an intoxication involving both 2-methyl-AP-237 and AP-238. PMID 37253676

The case reinforces two key principles:

1. users can be exposed to more than one novel opioid;
2. a symptom profile cannot reliably identify which cinnamylpiperazine is present.

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What overdose can look like

Expected opioid toxicity includes:

• severe sedation;
• inability to wake;
• slow/shallow breathing;
• apnea;
• blue/gray lips;
• pinpoint pupils;
• aspiration;
• collapse;
• cardiac arrest in severe poisoning.

Respiratory depression is the central life-threatening risk.

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Naloxone

Because 2-methyl-AP-237 and AP-238 activate MOR, naloxone is appropriate in suspected overdose.

There is no validated compound-specific bystander naloxone regimen.

Use available naloxone according to product/emergency guidance and call emergency services.

Mixed intoxication is common enough that:

• additional opioids;
• benzodiazepines;
• alcohol;
• other NPS

may remain clinically important even after opioid reversal.

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Metabolism of 2-methyl-AP-237

The 2023 fatal case identified three hydroxylated metabolites in blood and urine. PMID 37264551

Metabolite-aware testing matters because:

• parent drug can fall over time;
• unknown peaks may be missed;
• metabolism can extend the window of analytical confirmation.

The human metabolic literature remains much smaller than for conventional prescription opioids.

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Drug testing and detection

Routine opioid immunoassays should not be assumed to identify cinnamylpiperazine opioids reliably.

Published investigations relied on methods such as:

• GC-MS;
• LC-QTOF-MS;
• LC-MS/MS.

In the fatal 2-methyl-AP-237 case, the substance required advanced analytical work for confirmation.

Field-test limitation

The powder at the scene initially tested positive for fentanyl in a field test despite confirmatory laboratory analysis identifying 2-methyl-AP-237.

Field screening is useful triage.

It is not definitive structural identification.

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Tolerance

Repeated MOR agonism can produce opioid tolerance.

Direct controlled 2-methyl-AP-237 or AP-238 tolerance studies in humans are lacking.

Tolerance can encourage escalating exposure.

It can also create a false sense of safety: a person may feel less sedated while remaining vulnerable to:

• respiratory depression;
• batch variability;
• combinations with other depressants.

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Physical dependence

WHO's international scheduling review concluded that 2-methyl-AP-237 had dependence potential similar to other opioids such as morphine and fentanyl based on mechanism, effects and available reports.

That is an authoritative risk assessment—not a direct prospective dependence-incidence study.

For AP-238, direct human dependence data are even thinner.

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Withdrawal

No controlled study establishes a 2-methyl-AP-237- or AP-238-specific withdrawal timeline.

Expected opioid withdrawal can include:

• restlessness;
• anxiety;
• insomnia;
• sweating/chills;
• yawning;
• tearing/runny nose;
• abdominal cramps;
• nausea/vomiting;
• diarrhea;
• muscle aches;
• craving.

No validated home taper

An unregulated NPS product can vary in:

• concentration;
• identity;
• contaminants;
• co-opioids.

A self-designed taper based on seller claims therefore has an unstable foundation.

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Dependence vs opioid use disorder

Physical dependence means withdrawal occurs when exposure falls.

Opioid use disorder involves a broader pattern such as:

• craving;
• inability to cut down;
• escalating use;
• continued use despite harm;
• hazardous use;
• work/family problems;
• tolerance;
• withdrawal.

They are related but not identical.

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Treatment and support

There is no medication approved specifically for 2-methyl-AP-237 or AP-238 dependence.

When opioid dependence/OUD is present, clinicians use established opioid-use-disorder treatment principles.

Evidence-based medications include:

• buprenorphine;
• methadone;
• extended-release naltrexone in appropriate patients.

This article intentionally does not provide induction or taper dosing.

For U.S. resources:

• FindTreatment.gov
• SAMHSA National Helpline: 1-800-662-HELP (4357)

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Polysubstance risk

Fatal and nonfatal cases may include:

• benzodiazepines;
• fentanyl;
• other synthetic opioids;
• stimulants;
• alcohol.

The 2023 fatal case included alprazolam.

That matters because sedatives can compound impairment and respiratory risk.

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Forensic interpretation

A positive 2-methyl-AP-237 or AP-238 result does not by itself answer:

• how much was consumed;
• when it was consumed;
• whether the product label was accurate;
• whether another drug contributed;
• whether a measured concentration is universally lethal.

Postmortem concentrations are evidence for interpretation—not a dosing guide.

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Legal and regulatory history: 2-methyl-AP-237

International

WHO's 45th ECDD reviewed 2-methyl-AP-237 and concluded it had opioid effects, abuse/dependence potential and respiratory-depression risk comparable in kind to controlled opioids.

On March 15, 2023, the UN Commission on Narcotic Drugs voted unanimously to add 2-methyl-AP-237 to Schedule I of the 1961 Single Convention.

The decision entered into force for parties after UN notification on May 17, 2023. UNODC

United States

DEA permanently placed 2-methyl-AP-237 in Schedule I effective April 15, 2024.

DEA later issued a technical correction confirming that the Schedule I placement had been effective from that date despite numbering errors in the regulation. Federal Register correction

AP-238

AP-238 is a distinct compound.

Do not automatically apply 2-methyl-AP-237's Schedule I history to AP-238.

Legal status should be checked using:

exact compound + jurisdiction + date.

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Special populations

Direct controlled studies are absent for:

• pregnancy;
• breastfeeding;
• adolescents;
• older adults;
• respiratory disease;
• liver disease;
• kidney disease.

Risk is especially concerning for:

• opioid-naive people;
• people using benzodiazepines/alcohol;
• people using multiple novel opioids;
• people recently abstinent;
• people using alone.

No direct evidence is not evidence of safety.

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Myths and misconceptions

“2MAP is basically pharmaceutical bucinnazine.”

Misleading. It is a related derivative sold in an unregulated market without an approved modern formulation or safety program.

“It is weaker than fentanyl, so it is safe.”

False. Fatal intoxications are documented.

“AP-238 and 2-methyl-AP-237 are the same drug.”

False.

“The blood concentrations are much higher than nitazenes, so the risk is low.”

False. Concentration magnitude reflects pharmacology and kinetics; it does not imply safety.

“A fentanyl-positive field test proves fentanyl is the drug.”

Not necessarily. Confirmatory laboratory analysis is required.

“Because 2-methyl-AP-237 is Schedule I, AP-238 must be too.”

Not automatically. They are distinct molecules.

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What we know vs what remains unknown

Established

• both compounds activate MOR;
• human postmortem detections exist;
• 2-methyl-AP-237 has direct fatal intoxication evidence;
• AP-238 has authentic fatal/postmortem case evidence;
• advanced mass spectrometry can identify them;
• 2-methyl-AP-237 has international and U.S. Schedule I control.

Strongly plausible / class-supported

• tolerance;
• physical dependence;
• opioid withdrawal;
• loss-of-tolerance overdose risk;
• higher danger with other depressants.

Not established

• safe consumer dose;
• universal toxic/lethal concentration;
• controlled human PK;
• precise withdrawal timelines;
• validated self-taper;
• long-term safety;
• pregnancy safety;
• AP-238 legal status in every jurisdiction.

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Bottom line

2-Methyl-AP-237 and AP-238 are an important chapter in the post-fentanyl NPS story.

They show how illicit opioid markets can move into a completely different scaffold—the cinnamylpiperazines—while preserving the same core dangers:

• MOR-mediated respiratory depression;
• fatal overdose;
• unreliable product identity;
• polysubstance exposure;
• testing challenges;
• dependence and withdrawal risk.

The medicinal history of bucinnazine does not turn these unregulated derivatives into medicines.

The evidence-based harm-reduction stance is simple:

Treat them as opioids, treat suspected overdose as an opioid emergency, and do not convert forensic concentrations or receptor potency into a personal dosing rule.

Related evidence

• Designer synthetic opioids beyond nitazenes
• U-47700
• Brorphine
• Nitazene opioids
• Substance Use, Dependence & Harm Reduction hub