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Phenazepam was developed jointly by Odessa University and the USSR Academy of Medical Sciences, first synthesized in 1975 and adopted into Soviet clinical use by 1978, quickly becoming one of the most heavily prescribed benzodiazepines in the country. It was potent enough that tablets were dosed at fractions of a milligram, and it was issued as a standard component of civil-defense and security-force medical kits alongside its use for anxiety, insomnia, epilepsy and alcohol withdrawal. It stayed almost entirely unknown outside the former USSR until the 2000s, when it began appearing in Western Europe and the UK as an unregulated "research chemical," where its unfamiliar low-milligram potency led to a string of overdoses and eventual emergency scheduling under nicknames like "bonsai" and "the Soviet benzo."
- clinically used for decades in Russia for anxiety, insomnia, epilepsy and alcohol withdrawal
- issued as standard medical-kit medication for Soviet civil-defense and security forces
- substantially more potent per milligram than most Western benzodiazepines
- documented anticonvulsant activity in addition to anxiolytic effects
- high overdose risk, especially combined with opioids or alcohol
- its low-milligram potency has caused dosing miscalculations among Western users unfamiliar with it
- carries the same dependence and withdrawal risks as other benzodiazepines
- Phenazepam tablets were part of standard medical kits issued to Soviet civil-defense and security forces.
- It picked up the street name "bonsai" in parts of Western Europe after showing up as an unregulated research chemical decades after its Soviet development.
Mechanism
Classical positive modulator at the -A receptor benzodiazepine site, with substantially higher milligram-for-milligram potency than most Western benzodiazepines, producing pronounced sedative, anxiolytic, anticonvulsant and muscle-relaxant effects.
Safetyrisks and cautions, not medical advice
Phenazepam is an extremely potent, long-half-life benzodiazepine (active at roughly a tenth the dose of diazepam), which makes accidental overdose easy and dangerous; its delayed onset invites redosing before the first dose peaks. High doses produce muscle hypotonia, deep sleep, and coma, and numerous analytically confirmed fatalities have been reported, almost always in combination with other CNS depressants such as opioids or alcohol, where additive respiratory depression is the lethal mechanism.
It has a high potential for dependence and abuse, likely at the upper range of conventional benzodiazepines given its potency and duration, and withdrawal after heavy or prolonged use can be severe and unusually prolonged. Its long half-life also causes marked next-day sedation and impaired driving/psychomotor function. Because dosing is measured in fractions of a milligram, the margin for error is very small and precise measurement is critical.
History
Synthesized in 1975 (Odessa State University / USSR Academy of Medical Sciences); adopted into Soviet clinical and military-medical use from 1978 onward; remained essentially unknown in the West until it surfaced as an unregulated designer drug in the 2000s, after which it was brought under control in the UK, US and other jurisdictions.
Subjective profileweighing the evidence above
A genuinely potent, clinically real Soviet benzodiazepine whose decades of Cold War isolation ended only when it resurfaced as a grey-market drug people were dosing without any sense of its strength.
Resources
This entry is here for reference.
Research
- 1.Color-Coding Method Reveals Enhancement of Stereotypic Locomotion by Phenazepam in Rat Open Field Test
- 2.In vitro γ-aminobutyric acid A (GABA(A)) receptor activity and binding interactions at the α(+)/γ(2)(-) interface of 53 prescription and designer benzodiazepines.
2 listed here; entry last updated August 2026
Reviews
My notesprivate to this device
FAQ
How strong is phenazepam compared to diazepam?
It is considerably more potent per milligram, with clinical tablets historically dosed around 0.5-1 mg; this mismatch with typical Western benzodiazepine dosing habits has contributed to overdoses when it circulates as an unregulated research chemical.
Is phenazepam legal?
It is a controlled or scheduled substance in the US, UK and several other countries after emerging as a designer drug in the 2000s; it remains a licensed medicine only in Russia and some former Soviet states.
Adverse effects
- high overdose risk, especially combined with opioids or alcohol
- its low-milligram potency has caused dosing miscalculations among Western users unfamiliar with it
- carries the same dependence and withdrawal risks as other benzodiazepines
Notes and cautions
- now a controlled or scheduled substance in many countries outside Russia