Fluorophenibut (F-Phenibut)
Fluorophenibut is a fluorinated analogue of phenibut sold as a research chemical and unregulated nootropic for anxiolysis and sociability. It is presumed to act like phenibut as a GABA-B agonist and alpha-2-delta ligand, reportedly with faster onset. Human data are essentially nonexistent; the main documented risks are dependence and a difficult withdrawal, extrapolated from phenibut.
01 Overview
Marketed under names like fluorophenibut or F-phenibut and sometimes conflated with 4-fluorophenibut, it is a designer analogue of phenibut with no medical approval and no controlled human studies. Anecdotal reports describe anxiolysis, relaxation and mild euphoria with a quicker onset than phenibut.
The overriding concern is that, like phenibut, regular use produces tolerance and a severe rebound anxiety and insomnia withdrawal, which users frequently underestimate given the lack of formal characterisation.
02 Mechanism
Presumed GABA-B receptor agonism plus binding to the alpha-2-delta subunit of voltage-gated calcium channels, by analogy to phenibut; not experimentally confirmed for this analogue in humans.
03 Dosing
| Tier | Dose | Route | Notes |
|---|---|---|---|
| Reported anecdotal | 100–250 mg | Oral | Anecdotal; reported as more potent than phenibut. No safety data. |
04 Effects
| Effect | Magnitude | Evidence | |
|---|---|---|---|
| Anxiolysis and relaxationUsers describe reduced anxiety and social ease similar to phenibut with faster onset. | Reported | Anecdotal | |
| Mild euphoria / sociabilityReported mood lift and increased talkativeness at moderate doses. | Reported | Anecdotal |
05 Side effects
| Effect | Severity | Frequency | Evidence | Countermeasures |
|---|---|---|---|---|
| Dependence and withdrawalRebound anxiety, insomnia, tremor and agitation on cessation after repeated use. | Severe | Common with regular use | Anecdotal | |
| Oversedation with depressantsCombining with alcohol or benzodiazepines may cause dangerous CNS depression. | Severe | Unknown | Unconfirmed |