Phenibut

beta-phenyl-gamma-aminobutyric acid

Fenibut, Phenybut, PhGABA, Noofen, Anvifen

Psychoactive Class

Chemical Class

Phenibut is a depressant and anxiolytic of the gabapentinoid class, structurally derived from the neurotransmitter GABA. Developed in the Soviet Union during the 1960s under Professor V. V. Perekalin, it remains a prescribed pharmaceutical in Russia for conditions including anxiety, insomnia, depression, and PTSD. Outside Russia, it is unapproved for clinical use and typically sold as a nutritional supplement.¹² At common doses, it is noted for producing less drowsiness than other GABAergic substances such as benzodiazepines.

Dosage & Duration

Dosage

Threshold~0.25 g

Light0.5-1 g

Moderate1-2 g

Strong2-3.5 g

Heavy3.5+ g

The onset of effects is considerably slower than most other central nervous system depressants. To reduce the risk of accidental overdose, a minimum interval of two to three hours should be observed before considering any additional dose.

Duration

Onset1.5-3 hours

Come Up1.5-3 hours

Peak3-4 hours

Offset4-6 hours

After Effects6-24 hours

Total10-16 hours

Half-life

~5.3 hours

Subjective Effects

In comparison to other commonly used GABAgenic depressants such as alcohol or benzodiazepines, this compound is significantly longer lasting, more euphoric and more recreational.

Physical

Respiratory depressionIncreased perspiration Motor control loss Stomach cramps DizzinessPhysical euphoriaIncreased blood pressure Temperature regulation loss Appetite enhancement

Cognitive

DisinhibitionThought deceleration Cognitive euphoria Motivation enhancement Anxiety suppressionAmnesia

Forked from Subjective Effect Documentation

by Josie KinsJuly 2016.

Reagent Testing

Loading reagent data

Expected colorimetric results are being prepared.

Pharmacology

Pharmacodynamics

Phenibut acts as a full agonist of the GABA-B receptor and as a blocker of α2δ subunit-containing voltage-dependent calcium channels (VDCCs), the latter mechanism being shared with gabapentinoids such as gabapentin and pregabalin.³ Phenibut's affinity for α2δ-containing VDCCs is higher than for the GABA-B receptor, and in rodent models, analgesic effects appear mediated by VDCC blockade rather than GABA-B agonism.³ Only (R)-phenibut has meaningful activity at GABA-B, while both enantiomers block VDCCs with similar potency.⁴³ At higher doses, phenibut loses its GABA-B selectivity and gains additional activity as a GABA-A receptor agonist.⁵ Phenibut has also been reported to increase calcium-dependent spontaneous release of GABA in vitro, and its effects on dopamine remain unclear, with conflicting reports regarding whether it meaningfully raises dopamine levels.⁶⁵

Pharmacokinetics

Phenibut is not significantly metabolized and is largely excreted unchanged in the urine, with approximately 63-65% of the dose recovered renally.⁷ Following a single 250 mg oral dose in healthy volunteers, the elimination half-life was approximately 5.3 hours.⁷

Metabolitesnone documented yet

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.

DissociativesStimulants

TripSit

Tolerance

Full Tolerance

Tolerance to the sedative-hypnotic effects develops rapidly, typically within a couple of days of continuous use. Some users report noticeable tolerance after a single week of daily dosing. The Russian clinical literature indicates the substance is intended for only a few weeks of continuous use at the same dose due to this rapid tolerance development. Notably, tolerance to different effects may develop at different rates—sedative effects diminish while nootropic effects may be preserved or even enhanced with chronic dosing.

Baseline Reset

Full baseline tolerance is typically restored within 7-14 days of abstinence. Neuroadaptive changes to GABA receptor systems, including downregulation of GABA-B receptors and alterations in benzodiazepine and GABA-A receptor binding, have been observed to normalize within 24-48 hours after cessation in animal studies, though complete functional recovery in humans may take longer.

Half Tolerance

Tolerance begins to decrease after cessation, though specific half-tolerance timelines are not well-established in the literature.

Cross Tolerance

GABAergic depressants (benzodiazepines, alcohol, GHB), Other GABA-B agonists (baclofen)

Harm Potential

Addiction & Dependence

Psychological

Moderate

Phenibut is moderately psychologically addictive, particularly with heavy or frequent use.⁸ The extended onset period can lead to compulsive redosing when users mistakenly believe the substance is not working, and rebound anxiety commonly drives continued use.⁹

Physical

Moderate

Physical dependence develops with daily or near-daily use, sometimes within weeks of regular dosing.¹⁰¹¹ Withdrawal symptoms can be severe and include anxiety, insomnia, tremors, agitation, rapid heartbeat, nausea, vomiting, irritability, and fatigue.¹⁰¹ Baclofen has been used successfully to treat phenibut dependence.¹¹²

Toxicity

Hepatic

Prolonged use at high doses may cause fatty liver disease; doses above 7 grams have been associated with fatty liver degeneration in overdose cases.¹³

Renal

Renal impairment has been reported in overdose cases; this is not a typical concern at standard doses.¹⁰

Gastrointestinal

Phenibut hydrochloride is highly caustic and may cause intestinal discomfort, diarrhea, and potentially lower digestive tract bleeding in sensitive users.

Hematological

Eosinophilia has been reported with prolonged high-dose use and in overdose cases.¹⁰

Psychosis Risk

Acute psychosis and visual/auditory hallucinations have been reported primarily as withdrawal symptoms in recreational users discontinuing heavy use, rather than during intoxication.¹⁴ Withdrawal-associated psychosis appears to occur in cases of abrupt cessation following prolonged high-dose use.¹⁰¹

Seizure Risk

Tonic-clonic seizures have been reported in recreational users who have overdosed.¹⁵ Seizures are not a typical occurrence at standard doses and appear to be associated with significant overdose.¹⁰

History & Culture

Development and Soviet Adoption

Phenibut was synthesized during the 1960s at the Department of Organic Chemistry at the Al Gertsen Leningrad Pedagogical Institute under the supervision of Professor V. V. Perekalin.⁵ Following its development, the compound was researched for potential…

Legality

By Country

United StatesFederally uncontrolled

Not a federally scheduled substance. Legal to possess without license or prescription. Sales, distribution, and labeling are regulated by FDA rules when sold for human consumption.²² Note that Alabama classified phenibut as a Schedule II controlled substance at the state level as of November 21st, 2021.²³

CanadaUncontrolled

Not a controlled substance under Canadian law. Legal to possess without license or prescription.

ItalySchedule 1

Classified as a Schedule 1 controlled substance.¹⁹ Possession, production, and distribution are prohibited.

RussiaApproved pharmaceutical

Added to the State Drug Register in 1974 under Order No. 1126 by the USSR Ministry of Public Health.⁵ Remains available as a neuropsychotropic medication for conditions including anxiety, depression, PTSD, insomnia, and vestibular disorders.

United KingdomNot specifically controlled

Not a controlled substance under the Misuse of Drugs Act 1971. However, production, supply, or importation may potentially be prohibited under the Psychoactive Substances Act 2016,²¹ which applies blanket restrictions on psychoactive substances with exemptions for alcohol, nicotine, and medicinal products.

AustraliaSchedule 9

Classified as a prohibited substance as of February 1st, 2018.¹⁸ Possession, importation, supply, and manufacture are illegal.

GermanyPotentially NpSG

May be controlled under the Neue-psychoaktive-Stoffe-Gesetz (New Psychoactive Substances Act) as of July 18, 2019.⁷ Whether this legislation applies to phenibut remains legally unclear.

LatviaPrescription medication

Available as an unscheduled prescription drug marketed under the brand name 'Noofen.'²⁰ Also sold as 'Cognifen' in combination with ipidacrine for cognitive impairment associated with vascular disorders.

SwitzerlandNot controlled

Not listed under Buchstabe A, B, C, or D of controlled substances legislation. Generally considered legal to possess.

References

Source Pages

Citations

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Phenibut

beta-phenyl-gamma-aminobutyric acid

Fenibut, Phenybut, PhGABA, Noofen, Anvifen

Psychoactive Class

Depressant Anxiolytic GABAergic

Chemical Class

GABA analogue Gabapentinoid