Phenibut is generally well-tolerated.
Possible side effects may include sedation, somnolence, nausea, irritability, agitation, anxiety, dizziness, headache, and allergic reactions such as skin rash and itching.
At high doses (over 4-5 grams), motor incoordination, loss of balance, and hangovers, vomiting may occur. There are no specific antidotes for phenibut overdose. Management of overdose includes activated charcoal, gastric lavage, induction of vomiting, and symptom-based treatment. We are not aware about any cases of death in association with phenibut overdose.
However it is strongly advised not to take this medication together with other stimulants including alcohol.
Tolerance develops to phenibut with repeated use.
Withdrawal symptoms may occur upon discontinuation, and, in recreational users taking high doses, have been reported to include severe rebound anxiety, insomnia, anger, irritability, agitation.