Phenazepam
Phenazepam is a potent, long-acting benzodiazepine developed in the Soviet Union in the 1970s and still used medically in Russia and some post-Soviet states. Elsewhere it spread as a research chemical and drug of misuse. It is strongly sedating with a long half-life, and has been implicated in many intoxication and overdose deaths, especially in combination with opioids or alcohol.
01 Overview
Phenazepam is prescribed in Russia for anxiety, epilepsy, and alcohol withdrawal, so it has more human data than most designer benzodiazepines. Outside those markets it became widely available online and has featured in numerous forensic reports of severe intoxication, prolonged unconsciousness, and death.
It is highly potent by weight and long-acting, with slow onset that encourages redosing and a duration that leads to accumulation. Its involvement in fatalities is strongly associated with combined use with other depressants. Dependence and a difficult, protracted withdrawal are well recognised with regular use.
02 Mechanism
Positive allosteric modulator at the GABA-A benzodiazepine site, enhancing inhibitory neurotransmission; long duration due to slow clearance.
03 Dosing
| Tier | Dose | Route | Notes |
|---|---|---|---|
| Threshold | 0.25–0.5 mg | Oral | Slow onset; wait before considering more. |
| Common | 0.5–1 mg | Oral | Strong, long-lasting sedation and anxiolysis. |
| Strong | 1–2 mg | Oral | Heavy sedation; high accumulation and overdose risk. |
04 Effects
| Effect | Magnitude | Evidence | |
|---|---|---|---|
| AnxiolysisMarked anxiety reduction; used clinically for anxiety in some countries. | strong | Observational | |
| Sedation and hypnosisPronounced, long-lasting drowsiness. | strong, prolonged | Observational | |
| Anticonvulsant effectUsed adjunctively for epilepsy in Russia. | clinically used | Observational |
05 Side effects
| Effect | Severity | Frequency | Evidence | Countermeasures |
|---|---|---|---|---|
| Overdose and prolonged unconsciousnessHigh potency and long duration have caused many cases of deep, prolonged intoxication and death, especially with other depressants. | Life-threatening | Uncommon but well-documented | Observational | |
| Dependence and protracted withdrawalDependence develops readily; withdrawal is prolonged and can include seizures and delirium. | Severe | Common with regular use | Observational | |
| Accumulation and prolonged impairmentLong half-life causes carryover sedation and cognitive impairment. | Moderate | Common | Observational |