Phenobarbital - Substance Search

Summary TheDrug.Wiki TripSit PsychonautWiki

Phenobarbital is a long-acting barbiturate with extremely slow elimination and a narrow therapeutic window. It binds to a distinct allosteric site on GABA-A receptors separate from benzodiazepines, making combinations particularly dangerous as effects potentiate multiplicatively. Tolerance develops rapidly but not to lethal doses, narrowing the safety margin.

Dose Information TheDrug.Wiki TripSit PsychonautWiki

ROA	Light	Common	Strong	Heavy
Oral	50-100mg	100-150mg	150-300mg	300mg+

Light Common Strong Heavy

Onset, Duration & After-effects TheDrug.Wiki TripSit PsychonautWiki

ROA	Onset	Comeup	Peak	Offset	After Effects
Oral	15-60 min	1-2 hrs	4-6 hrs	12-24 hrs	1-48 hrs
Intravenous	5 min	-	15-30 min	12-24 hrs	1-48 hrs

Tolerance

Build-up develops over 1–4 weeks of daily use; hypnotic tolerance faster than anxiolytic tolerance

Reset weeks to months depending on half-life and duration of use; taper recommended

Tolerance Decay

Full tolerance 14d Half tolerance 7d Baseline ~21d

Tolerance to sedative effects typically builds with regular daily use over 1–2+ weeks and decays slowly over several weeks; data are largely clinical experience and user reports rather than controlled studies. Cross-tolerance with other positive GABAA modulators (e.g., benzodiazepines) is partial but clinically relevant. Because of phenobarbital’s long half-life, perceived tolerance may reflect accumulation rather than receptor-level changes.