Quick Summary

  • The half-life of phenibut is 5.3 hours
  • The duration of effects of phenibut is about 6 hours
  • It takes about 24 hours for phenibut to be eliminated from your body
  • Phenibut is a Russian drug that’s pharmacologically very similar to baclofen
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There are many reasons that you might be curious about phenibut’s half-life. For example, you might be wondering how long you should expect to feel the effects of phenibut or the amount of time it will take to be eliminated from your system.

Knowledge of drug half-lives is also a good way to time taking additional doses. For example, physicians often recommend patients take drugs with short half-lives in divided doses throughout the day. There’s also a correlation between half-life and addictive potential. Drugs with shorter half-lives are more likely to be abused.

What’s a half-life? The half-life of a drug is the interval of time it takes for the drug concentration to be reduced by 1/2. This concept is also used outside of pharmacology. For example, in nuclear physics radioactive decay is expressed as a half-life.

It turns out that the half-life of phenibut is about 5.3 hours. This assertion is based on a passage in Phenibut (beta-phenyl-GABA): a tranquilizer and nootropic drug By Lapin1.

PB was administered orally to healthy volunteers at a single dose of 250 mg. 65% of the dose was recovered unchanged in the urine. The plasma half-life of PB was 5.3 h. Its renal clearance approximated creatinine clearance.

Time (h) Percent Phenibut remaining (%)
5.3 hours 50%
10.6 hours 25%
15.9 hours 12.5%
21.2 hours 6.125%

When the drug concentration falls below 5% then we treat it is as being effectively out of your system. It takes about 21 hours to eliminate 94% of the phenibut in your body. However, the subjective effects of phenibut (e.g., anxiolysis) only last about 6 hours.


  1. Lapin I. Phenibut (beta-phenyl-GABA): a tranquilizer and nootropic drug. CNS Drug Rev. 2001;7(4):471-81.