What’s the best phenibut dosage? Unfortuntaely, there’s no one-size-fits-all answer. It depends on what you intend to accomplish with phenibut.Phenibut is useful as a nootropic agent (cognitive enhancer) but also as an anxiolytic. Optimal phenibut dosages for nootropic purposes are 10x lower than for anxiety relief. As with most drugs, less is more (dosage-wise).


  • The ideal phenibut dosage for nootropic effects is 25 – 50 mg.
  • The deal phenibut dosage for anxiolytic/tranquilizing effects is 250 – 500 mg.
    • Many individuals are routinely taking as much as 10x the recommended dose for anxiolysis which represents a serious safety hazard.

Phenibut gets a bad rap in the nootropics community because it has recreational potential, is frequently misused, and also has GABAergic effects which can impair memory. Nevertheless, phenibut does have some legitimate uses if caution is exercised.

Part of the controversy stems from the definition of a nootropic. Nootropics are defined by two criteria:

  • Enhancement of cognition function in at least one capacity (e.g., attention, working memory).
  • The absence of harm or ill-health effects at nootropic dosages.

I personally do not believe that phenibut is harmful at nootropic doses (25 – 50 mg). However, phenibut is unquestionably dangerous at recreational doses. Below, I’ll go into some case reports of individuals who overdosed on phenibut due to excessive dosages.

Health Risk of Excessive Phenibut Dosages

  • Phenibut overdose (may require hospitalization)
  • Addiction
  • Rebound anxiety on discontinuation
  • Downregulation of GABA receptors (theoretically)

The risk of phenibut addiction should not be overlooked. Here’s one excerpt from one Erowid user’s phenibut experience report:

After an extended period of use I lost the ability to restrict my use of the drug. Tolerance built to the point that the amount required to reach euphoria became so high that I was experiencing highly unpleasant gastrointestinal issues including diarrhea, painful stomach problems likely resulting from the high acidity, and frequent bouts of vomiting.

One bluelight user reports taking greater than 20 g doses of phenibut per day.

Excessive Phenibut Dosages

Some reckless people appear to be cavalier about phenibut dosages, taking as much as 2-5 g. Reading other’s anecdotal reports of the recreational use of phenibut may impart a false sense of security or that it’s safe to misuse phenibut and take high doses. Phenibut is dangerous at high doses and has led to a number of hospitalizations. For this reason, phenibut posts on /r/nootropics are marked with the high-risk tag.

Case Report 1: Phenibut Toxicity After Ingestion of 3g/Day

Excerpt from Phenibut, the appearance of another potentially dangerous product in the United States1.

We report a patient who reportedly suffered toxicity after using a novel substance named phenibut (β-phenyl-γ-aminobutyric acid). A 25-year-old male with a history of ethanol dependence and depression was found by his roommate to be unconscious and minimally responsive. For the past four days the patient had reportedly been ingesting internet-purchased phenibut at a dose of 1.5 grams twice daily.

Case Report 2: Development of Phenibut Addiction

Excerpt from Phenibut dependence2.

While phenibut was helpful initially, the patient developed dependence including tolerance, significant withdrawal symptoms within 3–4 h of last use and failure to fulfil his roles at work and at home. He finally sought medical assistance in our addictions clinic. We have gradually, over the course of 9 weeks, substituted phenibut with baclofen, which has similar pharmacological properties, and then successfully tapered the patient off baclofen. This required approximately 10 mg of baclofen for each gram of phenibut.

Case Report 3: Phenibut Toxicity Reported in Two Patients

Excerpt from Acute behavioural disturbance associated with phenibut purchased via an internet supplier3.

A 20-year-old female presented to the emergency department (ED) having used phenibut the prior day. The main finding was a decreased level of consciousness, however when roused she became delirious. Supportive care only was required with no specific intervention. The patient made a full recovery over a 24-hour period and admitted to use of phenibut purchased online. Plasma phenibut concentration was 29.7 μg/ml. A 38-year-old male presented to ED with an agitated delirium. The prior evening he had used tetrahydrocannabinol or THC, alcohol and phenibut, the latter purchased via the internet. His behavioural state had a suboptimal response to parenteral sedation. He was subsequently intubated for airway protection in the context of ongoing sedation to optimally manage his behavioural state. Post extubation the next morning he admitted using phenibut. Plasma phenibut concentration was 36.5 μg/ml.

The Nootropic Dosage of Phenibut

Nootropic (cognitive enhancing) effects of phenibut were reported to occur at the low dosages of 5 to 10 mg/kg in mice. This corresponds to a dose of 0.42 – 0.84 mg/kg in humans or about 25 – 50 mg for a 60 kg individual. Dosages in mice are adjusted to humans with an equivalent surface area dosage conversion factor.

Nootropic (cognition enhancing) activity. In the passive avoidance test in mice PB at small doses (5 to 10 mgGkg i.p.) facilitated formation of the conditioned reflex (38). The latency for the entry into the dark section of a chamber was 91 ± 154 sec in control an- imals and 284 ± 45 sec in animals treated with 5 mgGkg i.p. of PB ( p < 0.05). The total time spent in the dark part of the chamber was 108 ± 28 sec in control animals and 38 ± 12 sec in PB-treated animals ( p < 0.02). In addition, PB antagonized the amnestic ef- fects of chloramphenicol, 100 mgGkg i.p. At doses of 10 to 20 mgGkg i.p. PB enhanced the performance of mice in the swimming and rotating rod tests (38). Chronic administration of PB (50 mgGkg i.p., twice daily for 5 days) promoted a tolerance to its sedative action on the last day of treatment while its nootropic effect was enhanced.

The Tranquilizing Dosage of Phenibut

Phenibut elicits sedation in mice at 50 – 100 mg/kg or 4.2 – 8.4 mg/kg in humans. For a 60 kg individual, this range corresponds to 250 – 500 mg.

Tranquilizing effect. In mice, PB, at 50 to 100 mgGkg i.p., suppressed emotional re- action to pain induced by electrical stimulation. It also had an anxiolytic effect in the con- flict situation test. Diazepam (DZP) produced similar effects at 0.5 to 1.0 mgGkg i.p. In the elevated-plus maze a DZP-like tranquilizing effect was observed with PB, at 10 to 25 mgGkg i.p. (38). In the social interaction test PB at 10 to 50 mgGkg i.p. (unlike DZP, 1 mgGkg i.p.) did not increase the rate or duration of contacts in pairs of mice (34).

The Anxiolytic Dosage of Phenibut

Phenibut produces anxiolytic (anti-anxiety) effects at about the same dosage range as its tranquilizing effects: 250 – 500 mg. At extremely high doses phenibut inhibits aggression, but also impairs coordination at these dosages.

The anxiolytic effect of PB appears to be dependent on the emotional reactivity of the animals. In anxious and passive cats, PB abolished or suppressed fear and brought about an aggressive reaction to provocation. In aggressive cats PB had no effect on aggression. In non-aggressive cats without obvious fear, PB expanded the scope of positive emotional symptoms. In experimental models of fear induced by electrical stimulation of the hypothalamus or by peripheral aversive stimulation, PB had a selective antiphobic action and facilitated escape from stressful situations. This action was not asso- ciated with sedative or muscle relaxant effects. It was suggested that the antiphobic effect of PB is mediated by a GABA-mimetic action. In mice, aggressiveness induced by elec- trical stimulation was antagonized by PB but only at very high doses (300 mgGkg i.p. and higher). At these high doses PB inhibited motor coordination.

  1. O’connell CW, Schneir AB, Hwang JQ, Cantrell FL. Phenibut, the appearance of another potentially dangerous product in the United States. Am J Med. 2014;127(8):e3-4. 
  2. Samokhvalov AV, Paton-gay CL, Balchand K, Rehm J. Phenibut dependence. BMJ Case Rep. 2013;2013 
  3. Downes MA, Berling IL, Mostafa A, Grice J, Roberts MS, Isbister GK. Acute behavioural disturbance associated with phenibut purchased via an internet supplier. Clin Toxicol (Phila). 2015;53(7):636-8.