3-HO-PCP
3-hydroxyphencyclidine
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3-HO-PCP (3-hydroxyphencyclidine) is a synthetic dissociative of the arylcyclohexylamine class. It is a hydroxylated structural analog of PCP, distinguished by potent opioid receptor activity. 3-HO-PCP is both an NMDA receptor antagonist and a μ-opioid agonist, producing its effects by blocking glutamate signaling while simultaneously activating the brain's opioid system.[1][2]
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Synthesized in 1978 as part of systematic structure-activity studies of PCP derivatives,[1] 3-HO-PCP spent decades as a laboratory radioligand for mapping brain receptor sites.[3][4] It appeared on the research chemical market around 2009 and has since been detected in 27 countries.[5] The WHO Expert Committee on Drug Dependence reviewed 3-HO-PCP for possible international scheduling in October 2024.
Subjective effects include perceptual disconnection, derealization, analgesia, euphoria, and cognitive alteration. The experience is defined by an opioid warmth and sedation layered over dissociative detachment — a combination not found in other commonly available arylcyclohexylamines like ketamine or 3-MeO-PCP. Nausea, motor impairment, and confusion are common unsought effects.
μ-Opioid agonism predicts physical dependence with repeated use,[1] and no lethal dose has been established in any species.[5] The dual NMDA/opioid mechanism creates compound respiratory depression risk beyond what either pathway produces alone,[6] while NMDA antagonism carries psychotomimetic risk including hallucinations and paranoia.[7] No controlled human studies have been conducted; the current understanding rests on receptor binding data, forensic casework, and class analogy.
History[edit]
Discovery
3-HO-PCP was first synthesized in 1978 by Kalir and colleagues during systematic structure-activity studies of phencyclidine derivatives.[1] The compound drew pharmacological interest in the 1980s when binding studies revealed it possessed significant μ-opioid activity — a property absent in PCP itself.[4] By 1988, tritium-labeled 3-HO-PCP had become a standard radioligand for mapping NMDA and sigma receptor binding sites in animal brain tissue,[3] and autoradiographic studies through the 1990s used it to chart the distribution of NMDA receptor complexes across brain regions.[8][9]
Research chemical emergence
In 1999, an anonymous chemist posted observations on The Hive forum highlighting 3-HO-PCP's dramatically increased potency relative to PCP and its enhanced opioid activity[1] — the earliest documented interest in the compound as a candidate for human use. It appeared on the research chemical market around 2009, with user reports on harm reduction forums preceding commercial availability.[1] Analytical confirmations of law enforcement seizures followed in Denmark[10] and the United Kingdom.[11]
International spread and regulatory review
As of 2024, 3-HO-PCP has been reported in 27 countries across Europe, North America, Asia, and Oceania.[5] Sweden banned the compound in 2018,[1] and in October 2024 the WHO Expert Committee on Drug Dependence reviewed it for possible international scheduling under the 1971 Convention on Psychotropic Substances.[5] The outcome of that review has not been publicly confirmed.
The name "3-HO-PCP" follows standard arylcyclohexylamine nomenclature: "3-HO" denotes the hydroxyl group at the 3-position of the phenyl ring, and "PCP" identifies the parent phencyclidine scaffold. No widely adopted street names have emerged — the compound circulates almost exclusively under its chemical abbreviation.
Chemistry[edit]
Structural class
3-HO-PCP belongs to the arylcyclohexylamine family — the same chemical class as PCP, ketamine, and 3-MeO-PCP. The shared scaffold consists of a cyclohexane ring bonded to both an aromatic ring and an amine group. In 3-HO-PCP, the amine is a piperidine ring (shared with PCP), and the distinguishing feature is a hydroxyl group at the 3-position of the phenyl ring — replacing PCP's unsubstituted phenyl.[1]
This hydroxyl substitution is pharmacologically consequential: it confers substantial μ-opioid affinity absent in PCP. 3-HO-PCP is also a confirmed metabolite of 3-MeO-PCP, produced when the body removes the methyl group from 3-MeO-PCP's methoxy substituent.[12]
Molecular identity
| Molecular formula | C₁₇H₂₅NO |
| Molecular weight | 259.4 g/mol |
The molecule contains a cyclohexane ring bearing a piperidine nitrogen and a 3-hydroxyphenyl group.[13] The phenolic hydroxyl group acts as both a hydrogen bond donor and acceptor, influencing which receptors the molecule binds and how the body metabolizes it.
Stereochemistry
3-HO-PCP has one chirality center and is sold as a racemic mixture (equal mixture of both mirror-image forms). No published data compare the pharmacological activity of the individual enantiomers. By analogy with PCP and related compounds, the two forms likely differ in receptor preference, but this has not been studied for 3-HO-PCP specifically.citation needed
Physical properties
Available vendor descriptions report 3-HO-PCP as a white-to-off-white crystalline powder. No peer-reviewed data on melting point, solubility, or chemical stability have been published. The hydroxyl group makes the compound susceptible to metabolic conjugation reactions that the methoxy structural analog 3-MeO-PCP does not undergo directly.[10]
Pharmacology[edit]
Mechanism of action
3-HO-PCP blocks the NMDA ion channel at the same binding site as PCP, ketamine, and dizocilpine (MK-801).[2][14] The block is use-dependent — the compound binds preferentially when the channel is open, suppressing glutamate-driven excitatory signaling in a voltage- and activity-dependent manner.[1]
Unlike most arylcyclohexylamines, 3-HO-PCP simultaneously activates μ-opioid receptors with significant potency.[1][6] This dual profile — NMDA blockade plus opioid activation — is unique in the class and accounts for the compound's distinctive warmth, analgesia, and respiratory depression risk.[2] Additional activity at sigma-1 receptors and κ-opioid receptors further broadens the pharmacological profile beyond pure NMDA antagonism.[1]
This dual mechanism is predicted to amplify both CNS and respiratory depression relative to either drug class alone, contribute analgesic effects beyond NMDA antagonism, and confer higher physical dependence liability than pure dissociatives.
3-HO-PCP is a confirmed metabolite of 3-MeO-PCP, formed by removal of the methoxy group.[12] Users of 3-MeO-PCP are therefore exposed to 3-HO-PCP as a biotransformation product, complicating the pharmacological interpretation of 3-MeO-PCP's effects.
Pharmacokinetics
No controlled human pharmacokinetic study has been published. All available human data derive from a single forensic analytical study using Danish law enforcement and casework samples.[10]
Approximately 72% of circulating 3-HO-PCP is unbound to plasma proteins, meaning most of the drug is free to cross into the brain.[10] Postmortem analysis confirmed a brain-to-blood ratio of approximately 1.5, consistent with ready CNS penetration.[10]
Four metabolites have been identified in laboratory incubation with human liver cells: a hydroxylated piperidine product, an N-dealkyl carboxylic acid (the dominant urinary metabolite), a glucuronide conjugate, and a sulfate conjugate.[10] The specific liver enzymes responsible have not been determined for 3-HO-PCP, though related compounds are metabolized by CYP2B6, CYP2C19, CYP2D6, and CYP3A4.[12][15]inferred
Elimination half-life, oral bioavailability, and peak plasma concentration have not been determined in humans.
Neuroscience[edit]
Where it acts
NMDA blockade disrupts the normal flow of excitatory glutamate signaling, particularly in cortical circuits that coordinate perception, memory, and sense of self.[14][2] Radioligand mapping in animals shows 3-HO-PCP binds most densely in the hippocampus, superficial cortical layers, amygdala, and thalamus[8][9] — regions central to memory formation, sensory filtering, and emotional processing.
This distribution aligns with the dissociative, amnestic, and derealization effects observed across the NMDA antagonist class. The concurrent μ-opioid activation engages the brain's descending pain modulation pathway and the mesolimbic reward circuit, producing analgesia and euphoria on top of the dissociative state.[6][1]
Why it matters
3-HO-PCP intersects with the glutamate hypothesis of psychosis, which holds that NMDA receptor underactivity — whether from drugs or disease — can produce hallucinations, paranoia, and disordered thinking that model aspects of schizophrenia.[7][14] The compound's additional opioid activity may produce a qualitatively distinct psychotomimetic profile, though this has not been studied.
Recent research on ketamine's antidepressant effects has revealed synergistic interactions between NMDA antagonism and opioid signaling.[6] Dopaminergic mesolimbic pathway involvement, documented for other PCP analogs,[16][17] suggests the compound may engage both hedonic (opioid-mediated) and motivational (dopamine-mediated) reward systems.
Several fundamental questions remain unanswered. Does the opioid component qualitatively alter the dissociative experience, or merely add warmth and analgesia on top of standard NMDA effects? Do the two mirror-image forms of the molecule divide their activity between NMDA and opioid receptors?
Subjective Effects[edit]
The 3-HO-PCP experience occupies unusual territory among dissociatives: a progressive disconnection from sensory and cognitive grounding, overlaid with a distinctly opioid warmth and bodily heaviness that most NMDA antagonists do not produce. At lower doses, the opioid character dominates — sedation, analgesia, and a diffuse euphoria that colors the emerging dissociation. At higher doses, full dissociative immersion takes over, with depersonalization and perceptual distortion intensifying while the opioid sedation deepens. Set and setting significantly modulate both the emotional tone and the degree of cognitive disruption at every level.
Compared to ketamine, the experience is longer, warmer, and more sedating, with a respiratory risk that ketamine does not carry. Compared to 3-MeO-PCP, 3-HO-PCP trades stimulation and mania risk for opioid-type sedation and physical dependence potential — a fundamentally different risk profile despite their structural kinship as metabolic relatives.
Effect Grid
At common doses (4–6 mg oral), the full dissociative experience manifests: significant perceptual disconnection, derealization, time distortion, and altered thought patterns characteristic of NMDA antagonism. The opioid component contributes a pronounced body warmth, sedation, and euphoria that intensifies the overall experience beyond what comparably potent pure dissociatives produce.
Physically, analgesia becomes substantial, motor coordination is markedly impaired, and nystagmus is likely. Speech may become slurred. The combination of dissociative and opioid effects creates significant functional impairment lasting several hours.
Modeled from the effect's dose-dependence curve — not per-substance measurements.
Perspective distortion · Visual haze / noise · Visual acuity suppression · Auditory distortion · Auditory misinterpretation · Dreaming suppression · Sensory deprivation · Touch suppression · Touch enhancement · Visual drifting · Music enhancement · Visual processing suppression · Internal hallucinations · Auditory hallucinations · External hallucinations · Environmental orbism / cubism · Shadow people · Visual scenery slicing · Olfactory hallucination
Auditory misinterpretation · Dreaming suppression · Sensory deprivation · Touch suppression · Touch enhancement · Visual drifting · Music enhancement · Visual processing suppression · Internal hallucinations · Auditory hallucinations · External hallucinations · Environmental orbism / cubism · Shadow people · Visual scenery slicing · Olfactory hallucination
Body high · Tactile euphoria · Body schema distortion · Muscle relaxation · Pupil constriction · Sedation · Stimulation · Appetite suppression · Sexual arousal suppression · Bodily heaviness · Constipation · Nausea · Spontaneous body sensations · Bodily lightness · Breathing alteration · Involuntary body movements · Laughter fits · Trembling · Restlessness · Dehydration sensation · Vomiting · Respiratory depression · Abnormal heartbeat · Excessive sweating · Increased urination · Bodily dissociation · Seizure threshold reduction
Muscle relaxation · Pupil constriction · Sedation · Stimulation · Appetite suppression · Sexual arousal suppression · Bodily heaviness · Constipation · Nausea · Spontaneous body sensations · Bodily lightness · Breathing alteration · Involuntary body movements · Laughter fits · Trembling · Restlessness · Dehydration sensation · Vomiting · Abnormal heartbeat · Excessive sweating · Increased urination · Bodily dissociation · Seizure threshold reduction
Focus suppression · Information processing suppression · Memory fragmentation · Memory suppression · Cognitive euphoria · Analysis suppression · Thought deceleration · Pattern recognition suppression · Immersion enhancement · Language suppression · Cognitive dysphoria · Delusions of sobriety · Conceptual thinking · Thought connectivity · Amnesia · Delirium · Delusions
Memory suppression · Cognitive euphoria · Analysis suppression · Thought deceleration · Pattern recognition suppression · Immersion enhancement · Language suppression · Cognitive dysphoria · Conceptual thinking · Thought connectivity · Amnesia · Delirium · Delusions
Dysphoria
Craving · Social disconnection · Cognitive disconnection · Boundary dissolution
Timeline
First subtle awareness of altered state — mild cognitive shift or faint bodily warmth from the opioid component. Effects are sub-threshold and easily attributed to expectation.
Dissociative and opioid effects build in tandem: increasing perceptual detachment, warmth spreading through the body, and mild euphoria. Motor coordination begins to decline.
Maximum dissociation and opioid effects converge — pronounced derealization, time distortion, analgesia, and sedative warmth. The dual pharmacological character is most evident at this phase.
Effects plateau at sustained but diminishing intensity. Dissociative character gradually recedes while opioid warmth and sedation persist. Cognitive function begins partial recovery.
Gradual return to baseline awareness. Residual sedation, mild analgesia, and cognitive fogginess may linger. Physical coordination is still impaired.
Residual warmth, mild mood elevation or flatness, and subclinical cognitive dulling may persist for several hours after the primary experience resolves.
⚠ Do not drive or operate machinery for at least 12 hours after ingestion, as residual dissociative and opioid impairment may persist beyond subjective awareness.
Safety[edit]
- Acute toxicity
- Moderate
- Chronic toxicity
- Moderate
- Withdrawal
- Moderate
- Tolerance buildup
- moderate
- Tolerance reset
- 10 days
- Physical
- Moderate
- Psychological
- Moderate
- Compulsive redosing
- Moderate
- Dose escalation
- Moderate
- Cross-tol.
- dissociatives · opioids
Toxicity
Acute toxicity
No lethal dose has been established for 3-HO-PCP in any species, and no preclinical toxicity studies have been published.[5] The toxic dose in humans is unknown, and no therapeutic index can be calculated.
The only analytically confirmed case of severe acute toxicity involved co-ingestion with N-ethylhexedrone (a synthetic cathinone) in the UK.[11] A postmortem case reported a blood concentration of 0.095 mg/kg, though multiple other substances were co-detected and causation was not established.[10] The WHO review concluded that in no fatal or nonfatal case was 3-HO-PCP the only substance detected.[5]
Respiratory depression
The combination of NMDA blockade with intrinsic μ-opioid activation creates compound respiratory depression risk beyond what either mechanism alone produces.[1][6] This is the most critical safety consideration distinguishing 3-HO-PCP from most other PCP analogs, which lack meaningful opioid activity.
All documented serious cases involved co-ingestion of other CNS depressants.[5]
Organ toxicity
No organ-specific toxicity studies have been published. Muscle breakdown and acute kidney injury have been documented in the PCP analog class,[18] making these plausible risks. No bladder toxicity analogous to ketamine-associated bladder damage has been reported, though chronic use data are absent.
Detection
Standard urine drug screens for PCP detect only about 20% of PCP structural analogs,[19] making 3-HO-PCP likely to produce a false-negative result. Confirmatory identification requires advanced mass spectrometry (LC-HRMS).[10]
Psychological risks
NMDA antagonism carries psychotomimetic risk: hallucinations, paranoia, emotional withdrawal, and disordered thinking — symptoms that model aspects of psychosis.[7][14] Heavy or chronic use of PCP-type compounds carries risk of persistent psychosis extending beyond the acute intoxication period.
No substance-specific data on the incidence or duration of 3-HO-PCP-induced psychosis exist, and the contribution of μ-opioid agonism to the psychotomimetic profile is unknown. No data on HPPD (HPPD) following 3-HO-PCP use have been published.
Tolerance & dependence
3-HO-PCP's dual pharmacology creates higher theoretical abuse liability than either mechanism alone.
μ-Opioid agonism predicts physical dependence with repeated use through the same receptor adaptation mechanisms as opioid drugs.[1] No published studies specifically confirm physical dependence for 3-HO-PCP, but the mechanism is well-established for the opioid class.
Dissociative-type psychological dependence via dopamine reward pathways is documented for other PCP analogs.[16][17] Specific tolerance kinetics have not been published. Provisional estimates of a 5.5-day tolerance half-life and approximately 1.5-week full reset have no identifiable primary source.safety citation needed
Drug interactions
CNS depressants — high risk
Opioids: 3-HO-PCP's intrinsic μ-opioid activity makes combination with any opioid particularly dangerous — the respiratory depression is synergistic, not merely additive.[1][5]
Benzodiazepines: Additive CNS depression and respiratory depression. All documented serious 3-HO-PCP cases involved co-present benzodiazepines.[5]
Alcohol: Additive CNS depression.[20]
Stimulants — elevated risk
Co-ingestion with N-ethylhexedrone (a synthetic cathinone) produced severe toxicity in the only analytically confirmed UK case.[11] Stimulant-dissociative combinations carry cardiovascular risk.
Enzyme inhibitors — class inference
By analogy with related compounds,[12][15] inhibitors of CYP2B6 (ticlopidine, clopidogrel), CYP3A4 (ketoconazole, certain antiretrovirals, grapefruit juice), and CYP2D6 (paroxetine, fluoxetine) may increase 3-HO-PCP plasma levels.inferred
Contraindications
No published study addresses contraindications specific to 3-HO-PCP. The following are inferred from its dual NMDA antagonist / μ-opioid agonist profile inferred:
Absolute (class-inferred):
- History of psychotic disorders or schizophrenia — NMDA antagonism can precipitate or worsen psychotic episodes[7][14]
- Respiratory insufficiency or compromised airway — intrinsic opioid activity compounds breathing depression risk
- Concurrent opioid use — synergistic respiratory depression[5]
Relative (class-inferred):
- History of opioid dependence — μ-opioid agonism may trigger relapse
- Liver impairment — enzyme-dependent metabolism may lead to elevated levels
- Concurrent benzodiazepine use — additive CNS and respiratory depression
- Heart conditions — arylcyclohexylamines can produce elevated heart rate and blood pressure
- Pregnancy and breastfeeding — no reproductive toxicity data exist
Harm Reduction[edit]
Forms & Identification
3-HO-PCP circulates almost exclusively as a white-to-off-white powder, occasionally pressed into pellets. At active doses of 1–8 mg, even small variations in powder weight translate to large differences in effect intensity — precision scales accurate to 1 mg are essential, not optional. The compound is visually indistinguishable from many other research chemicals including other PCP analogs of dramatically different potency.
Reagent testing can help rule out gross misidentification but cannot confirm identity or purity. Quantitative analysis through a drug checking service is the most reliable way to verify what a sample contains and at what concentration.
Guidelines
- Test every batch with reagent kits and, where available, a drug checking service
- Use a milligram-precision scale — volumetric dosing in solution is an alternative for sub-milligram accuracy
- Start with the lowest reported threshold dose and wait the full onset period before considering redosing
- Have a sober sitter present, particularly at unfamiliar doses
- Do not use alone — the opioid component means loss of consciousness carries respiratory risk
- Eat lightly beforehand; nausea is common
- Keep the environment physically safe — remove sharp objects and fall hazards, as motor coordination will be impaired
- Avoid redosing during the experience; the long duration means effects accumulate unpredictably
Set & Setting
Dissociative experiences are strongly shaped by psychological state and environment. A calm, familiar, low-stimulation setting with a sober sitter reduces the risk of panic, disorientation, and injury from impaired motor control.
The opioid warmth of 3-HO-PCP can create a false sense of safety and comfort, masking dose escalation and respiratory depression risk. Users accustomed to non-opioid dissociatives should not assume equivalent safety margins.
Aftercare & integration. The dissociative afterglow can persist for hours after primary effects resolve. Allow a full recovery day with no demanding tasks, driving, or operating machinery. Sleep, hydration, and light nutrition support recovery.
Dissociative experiences can surface unfamiliar psychological material — depersonalization, altered self-perception, or emotional suppression that persists beyond the acute window. Journaling or talking through the experience with a trusted person can help process these effects. If derealization, emotional numbness, or intrusive thoughts persist beyond 48 hours, professional support is warranted.
Recovery & Support
The μ-opioid agonism of 3-HO-PCP means physical dependence is a real possibility with repeated use — a risk most dissociative users do not anticipate. Escalating dose, using to avoid withdrawal discomfort, or difficulty maintaining intended breaks are signs of developing dependence.
Withdrawal from compounds with opioid activity may include physical symptoms (muscle aches, restlessness, insomnia, gastrointestinal distress) alongside psychological symptoms (anxiety, dysphoria, craving). Medical supervision for tapering is recommended. SAMHSA's National Helpline (1-800-662-4357) provides free, confidential referrals in the United States.
Recovery resources, crisis lines, and support pathways → View all
Emergency response
Recognizing an emergency:
- Breathing becomes slow, shallow, or stops
- Lips or fingertips turn blue or grey
- Person cannot be roused by voice or firm stimulation
- Severe confusion, agitation, or self-harm behavior
- Seizure activity
- Chest pain or irregular heartbeat
Immediate steps:
- 1. Call emergency services immediately if breathing is compromised or the person is unresponsive
- 2. Place the person in the recovery position (on their side) to keep the airway clear
- 3. If naloxone is available and breathing is dangerously slow, administer it — 3-HO-PCP's μ-opioid activity means naloxone may partially reverse respiratory depression.[1][6] Naloxone efficacy in 3-HO-PCP overdose has not been clinically validated safety citation needed
- 4. Do not leave the person alone; do not induce vomiting
- 5. Monitor breathing continuously until help arrives
What to tell the dispatcher: the substance name (3-HO-PCP, a dissociative with opioid activity), estimated amount, time of ingestion, and current symptoms. Good Samaritan laws in many jurisdictions protect people who call for help during a drug emergency.
Legal Status[edit]
3-HO-PCP is not currently subject to international scheduling under the United Nations conventions, though it was reviewed by the WHO Expert Committee on Drug Dependence (ECDD) at its 47th meeting in October 2024 for possible scheduling under the 1971 Convention on Psychotropic Substances.[5] National scheduling varies significantly by jurisdiction, with some countries having enacted specific bans while others rely on structural analog legislation.
| Jurisdiction | Classification | Key provisions |
|---|---|---|
| United States | Unscheduled (federal) | Not specifically listed under the Controlled Substances Act. Prosecutable under the Federal Analogue Act (21 U.S.C. §813) when intended for human consumption[21][1] |
| United Kingdom | Class B (Misuse of Drugs Act 1971) | Covered by the arylcyclohexylamine generic clause[1] |
| Canada | Schedule I (CDSA) | Controlled Drugs and Substances Act[1] |
| Germany | NpSG restricted | Industrial and scientific use only under the New Psychoactive Substances Act[1] |
| Sweden | Banned | Prohibited since 28 June 2018[1] |
| Switzerland | Banned | Specific scheduling[1] |
| International | Not under international control (as of early 2024) | WHO ECDD 47th meeting reviewed for possible scheduling under the 1971 Convention, October 2024[5] |
The US Federal Register notice of August 2024 solicited public comment on the WHO ECDD assessment of 3-hydroxyphencyclidine, indicating international scheduling was under active consideration.[21] The final outcome of the October 2024 ECDD review has not been publicly confirmed as of this writing.
references
- [1]
- [2] ^abcdLuethi D, Liechti ME (2020) Designer drugs: mechanism of action and adverse effects — Archives of Toxicology doi:10.1007/s00204-020-02693-7
- [3] ^abItzhak Y, Khouri M (1988) Regulation of the binding of sigma- and phencyclidine (PCP)-receptor ligands in rat brain membranes by guanine nucleotides and ions — Neuroscience Letters PMID:2834673
- [4] ^abItzhak Y (1988) Pharmacological specificity of some psychotomimetic and antipsychotic agents for the sigma and PCP binding sites — Life Sciences PMID:2893238
- [5]
- [6]