WARNINGMIXING OR WITHDRAWAL CAN BE DANGEROUS

Ordinary doses in combination with other depressants can fatally stop breathing. After prolonged regular use, stopping suddenly can also cause seizures or delirium; seek medical help.

Phenazepam

7-Bromo-5-(2-chlorophenyl)-1,3-dihydro-1,4-benzodiazepine-2-one

Bonsai, Soviet Benzo, Fenaz, Panda, Bromdihydrochlorphenylbenzodiazepine

Psychoactive Class

Depressant Anxiolytic GABAergic Muscle Relaxant

Chemical Class

Benzodiazepine

Phenazepam is a benzodiazepine first developed in the Soviet Union in 1975.¹² It is prescribed in Russia and other countries for psychiatric conditions including anxiety and schizophrenia, as well as for epilepsy, alcohol withdrawal, and surgical premedication.¹³ Phenazepam is notable for its exceptionally long duration of action and high potency.⁴² The substance has gained notoriety for problematic recreational use, with numerous reports of compulsive redosing and reckless behavior due to its subtle onset and extended effects.¹⁴

Dosage & Duration

Dosage

Doses are population estimates that vary widely between individuals.

Threshold~0.5 mg

Light0.5-1 mg

Moderate1-2 mg

Strong2-3 mg

Heavy3+ mg

Bioavailability

80%¹

Duration

Onset15-60 minutes

After Effects36 hours

Total18 hours

Subjective Effects

The experience is dominated by heavy sedation, anxiolysis, and physical relaxation, with no reported alteration of sensory perception. Coordination becomes unreliable, and at higher doses recall of the period following ingestion can be substantially impaired.

Physical

Muscle relaxation, drowsiness, and hypnotic sedation are the primary physical effects, accompanied by dizziness and loss of coordination.

Hiccups

Coordination

Dizziness

Sedation

Muscle relaxation

Cognitive

Anxiety is reduced and the mental state is markedly sedated, with anterograde amnesia becoming pronounced as dose increases.

Anxiety suppression

Reagent Testing

Expected colorimetric results for common reagent tests. Colors show reaction change over 1–2 minutes.

Marquis(MQ)

Mecke(ME)

Mandelin(MD)

No reaction

Ehrlich(EH)

No reaction

PROtestkit.eu

Pharmacology

Pharmacodynamics

Phenazepam acts as a positive allosteric modulator at the benzodiazepine site of the GABA-A receptor.¹⁵ It is considerably more potent than diazepam, potentiating GABA responses with an EC50 of 6.1 nM in rat cerebellar slices versus 13.5 nM for diazepam.¹ About 1 mg of phenazepam is reported to be equivalent to up to 10 mg of diazepam.¹ The metabolite 3-hydroxyphenazepam is also pharmacologically active and potentiates GABA responses.¹ The metabolites ABPH and QNZ exhibit biphasic activity at the GABA-A receptor, initially potentiating GABA at low concentrations and then inhibiting it at higher micromolar concentrations, so they are only likely to produce significant effects in overdose.¹ ABPH is also thought to act at glycine and NMDA receptors at high micromolar concentrations.¹

Pharmacokinetics

Phenazepam is eliminated primarily by hepatic metabolism, with combined in silico and in vitro evidence identifying CYP3A4 as the most probable enzyme responsible and CYP3A5 as a possible contributor that could not be excluded.⁵ The main pathway is aromatic hydroxylation to 3-hydroxyphenazepam, alongside hydrolysis and glucuronide conjugation.¹⁶ After oral administration, phenazepam reaches a peak plasma concentration at about 4 hours and has an estimated bioavailability of roughly 80%.¹ Its elimination half-life is reported between about 15 and 60 hours, spanning an oral estimate of roughly 60 hours and 14.9-15.6 hours following intramuscular or intravenous administration.¹ The volume of distribution is 4.7-6.0 L and plasma clearance is 220.4-267.9 ml/h.¹ In vitro, phenazepam also produced an observed but not statistically significant increase in CYP2B6 activity.⁵

Interactions

Dangerous

Highest risk

These combinations are considered extremely harmful and should always be avoided. Reactions to these drugs taken in combination are highly unpredictable and have a potential to cause death.

AlcoholGHB/GBLOpioidsTramadol

Unsafe

Avoid

There is considerable risk of physical harm when taking these combinations, they should be avoided where possible.

DiphenhydraminePCP

Caution

Use caution

These combinations are not usually physically harmful, but may produce undesirable effects, such as physical discomfort or overstimulation. Extreme use may cause physical health issues. Synergistic effects may be unpredictable. Care should be taken when choosing to use this combination.

DXMKetamineMXE

TripSit

Tolerance

Tolerance timelines are rules of thumb, not exact schedules, and vary widely between individuals and use patterns.

Full Tolerance

Tolerance develops with regular use.⁷³ Treatment courses are typically limited to two weeks due to the risk of dependence, suggesting clinically significant tolerance develops within this timeframe.

Cross Tolerance

Benzodiazepines⁸, GABAergic depressants⁸

Harm Potential

Addiction & Dependence

Psychological

High

High abuse potential with significant risk of psychological dependence.⁹ Anecdotal reports indicate a notable suggestibility for compulsive redosing and reckless usage patterns, particularly due to the drug's subtle onset and amnestic effects.⁹

Physical

High

Physical dependence develops with regular use, and treatment courses are typically limited to two weeks due to dependence risk.⁹⁷ Abrupt discontinuation following prolonged use can cause severe withdrawal symptoms including restlessness, anxiety, insomnia, seizures, convulsions, and potentially death.¹⁰⁷ Due to its intermediate half-life and active metabolites, withdrawal symptoms may take two or more days to manifest.⁹

Seizure Risk

Seizures and convulsions are documented withdrawal symptoms following abrupt discontinuation of prolonged use.¹⁰⁷ Gradual dose reduction is necessary to prevent withdrawal-induced seizures.¹⁰⁷

History & Culture

Phenazepam is a benzodiazepine that was first developed in the Soviet Union in 1975.⁹ The synthesis method was developed at the Physico-Chemical Institute of the Academy of Sciences of the Ukrainian SSR during the 1970s. The substance is now produced in Russia and several…

Legality

By Country

BelarusLegal (regulated)Republican list of narcotic drugs

Republican list of narcotic drugs, psychotropic substances and their precursors subject to state control in the Republic of Belarus (consolidated through Ministry of Health Resolution No. 18 of 10 March 2026)¹³

The current fetched Belarus list supports controlled circulation, but not the original specific indications for epilepsy or alcohol withdrawal.

ColombiaRestrictedLista Verde IV

Resolución 000116 de 2026¹⁶

Colombia lists fenazepam as a substance of special control and subject to fiscalization in Resolution 000116 of 2026. The resolution places it in Lista Verde, Lista IV, the national implementation of the international psychotropic control listing.

FrancePrescription onlyPsychotrope

Arrêté du 4 novembre 2016 modifiant l’arrêté du 22 février 1990 fixant la liste des substances psychotropes¹⁸

Le phénazépam figure sur la liste française des substances psychotropes. La liste consolidée de l’ANSM le rattache à l’arrêté du 4 novembre 2016 modifiant l’arrêté du 22 février 1990.

KazakhstanPrescription medication²¹

Legally prescribed for medical conditions including epilepsy and alcohol withdrawal syndrome.²¹ Available through licensed medical practitioners.

LithuaniaPrescription onlyFenazepamas (Phenazepam), item 18 in List III (psychotropic substances permitted for medical purposes), under the 1971 Convention IV list. A medicinal preparation containing a List III psychotropic is subject to the psychotropic-medicine prescription rules, including the special prescription form for paper prescriptions.

Lithuanian Minister of Health Order No. 5 of 6 January 2000, On Approval of the Lists of Narcotic and Psychotropic Substances, current consolidated edition effective 18 June 2025 (List III); Lithuanian Minister of Health Order No. V-700 of 29 July 2025 amending Order No. 112 on prescription writing and dispensing rules, effective 7 November 2025.²⁴²⁵²⁶

Corrected rather than supported: the legal core of the legacy row is corroborated, but the official sources inspected establish List III medical-use control and prescription handling, not the asserted indication-specific claim of epilepsy and alcohol-withdrawal treatment, nor current Lithuanian marketing or registration of a phenazepam product. Phenazepam should therefore be represented as prescription-only controlled psychotropic material, without asserting those indications or practical availability.

RussiaPrescription medication²⁸

Legally prescribed for medical conditions including epilepsy and alcohol withdrawal syndrome.²⁸ Available through licensed medical practitioners.

UkraineRestricted

Про затвердження переліку наркотичних засобів, психотропних речовин і прекурсорів, постанова Кабінету Міністрів України від 06.05.2000 № 770 (чинна редакція від 07.06.2026)³⁰

The official Ukrainian list supports restricted circulation, not the original broad statement that it is simply a prescription medication for specified conditions.

CanadaIllegal (analog/blanket ban)Schedule IV benzodiazepine

Controlled Drugs and Substances Act, Schedule IV, item 18¹⁴¹⁵

Phenazepam is covered by Schedule IV's category for benzodiazepines, their salts and derivatives. The Controlled Drugs and Substances Act prohibits unauthorized trafficking, importation, exportation, and production of Schedule IV substances. Schedule IV is not included in the Act's simple-possession prohibition, but obtaining a Schedule IV substance from a practitioner is regulated.

DenmarkRestrictedListe E item 33

Bekendtgørelse om euforiserende stoffer (BEK nr. 405 af 26. marts 2026), Bilag 1, Liste E, nr. 33¹⁷

Fenazepam is expressly listed in Liste E, nr. 33. Liste B, D og E omfatter stoffer, der kun må benyttes til medicinsk og videnskabelig brug. The regulation entered into force on 29 March 2026 and repealed BEK nr. 2446 of 12 December 2021.

GermanyPrescription onlyAnlage III

Betäubungsmittelgesetz, Anlage III¹⁹²⁰

Phenazepam is listed in Anlage III of Germany's Betäubungsmittelgesetz. Anlage III contains marketable and prescribable narcotic drugs; the statute regulates their traffic and prescription.

LatviaRestrictedIII List psychotropic

Annex 2, Law on the Coming into Force and Application of the Criminal Law²²²³

Phenazepam (Fenazepāms; CAS 51753-57-2) is named in Latvia's controlled-substances III List, for dangerous psychotropic substances liable to misuse. Latvia applies controls to listed substances and their derivatives, isomers, structural analogues, active metabolites, esters, ethers, salts, and medicines containing them; licensed pharmaceutical activity is required for dealings with III List substances and medicines.

NetherlandsIllegalList II

Opiumwet, lijst II²⁷

Phenazepam is listed as ‘fenazepam’ in List II of the Opiumwet, with the chemical description 7-bromo-5-(2-chlorophenyl)-1,3-dihydro-2H-1,4-benzodiazepin-2-one. Article 3 prohibits import, export, preparation, sale, supply, transport, possession and manufacture of List II substances.

SwedenIllegalNarkotika

Förordning (1992:1554) om kontroll av narkotika, bilaga 1²⁹

Phenazepam is listed as “fenazepam” in Annex 1 under sleeping and sedative substances. Section 2 provides that substances in Annex 1 are deemed narcotics under the Narcotic Drugs Criminal Act.

United KingdomIllegalClass C / Schedule 3

Misuse of Drugs Act 1971 and Misuse of Drugs Regulations 2001³¹³²

Phenazepam is controlled as a Class C drug under the Misuse of Drugs Act 1971 and in Schedule 3 to the Misuse of Drugs Regulations 2001. Its possession, supply, production, importation, and exportation are regulated under the United Kingdom's controlled-drugs legislation.

References

Source Pages

Citations

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