This is an experience report concerning 4F-Phenibut (Fluorobut). I have experimented with 4F-Phenibut and Phenibut occasionally (without ever creating tolerance) over the past several years.
4-Fluorophenibut
Limited data
Limited data
Sparse data. Doses and effects may be unreliable or untested.
- 3 corroborating sources
- 1 ROA with full dose ladder
- duration data present
- toxicity data (PsychonautWiki)
- classified Tentative
- classified Research-chemical
- dose data not in PW/TripSit (unverifiable)
- dose ladder unverifiable and undisclosed — capped
Limited data
Sparse data. Doses and effects may be unreliable or untested.
- 3 corroborating sources
- 1 ROA with full dose ladder
- duration data present
- toxicity data (PsychonautWiki)
- classified Tentative
- classified Research-chemical
- dose data not in PW/TripSit (unverifiable)
- dose ladder unverifiable and undisclosed — capped
Aliases: Baflofen, Fluorobut, Cgp-11130, F-phenibut, Fluorophenibut
Summary
4-Fluorophenibut (F-phenibut) is a depressant and anxiolytic GABA analogue, chemically a fluorinated analog of phenibut. It acts primarily as a potent GABA-B receptor agonist, in this respect resembling baclofen more than phenibut, with possible voltage-gated calcium channel activity. It is reported to be 5-10 times more potent than phenibut, with faster onset and shorter duration. Users report more pronounced physical effects and euphoria compared to phenibut, along with a correspondingly higher risk of dependence and compulsive redosing.
Dose Information
| ROA | Light | Common | Strong | Heavy |
|---|---|---|---|---|
| Oral | 100-150mg | 150-400mg | 400-600mg | 600mg+ |
Light
Common
Strong
Heavy
Sources
Oral
Dose ladder — dose.wikiOnset, Duration & After-effects
| ROA | Onset | Comeup | Peak | Offset | Total |
|---|---|---|---|---|---|
| Oral | 20-90 min | 30-60 min | 2-5 hrs | 2-4 hrs | 8-12 hrs |
Tolerance
Build-up
develops over 1–4 weeks of regular use
Reset
Falls after you stop, at a rate that varies from person to person. If you've been using regularly, cut down gradually with medical help rather than stopping suddenly.
No tolerance chart. Our decay curves for these drugs were estimates, and a curve can make tolerance look longer-lasting than it is, which is the dangerous direction.
How fast tolerance to these drugs fades after a break has not been measured well enough to draw, so don't count on a dose you used to take still being safe: after time off, start with a much smaller amount and don't use alone. Mixing sedatives with each other, with alcohol or with opioids sharply raises the risk of a fatal overdose. If you've been using regularly, don't stop suddenly: withdrawal from benzodiazepines, alcohol or GHB/GBL can cause seizures or delirium, so get medical help to cut down gradually.
Sources: FRANK: benzodiazepines · Alcohol and Drug Foundation: GHB · FDA 2020: benzodiazepine boxed warning · FDA 2019: gabapentinoids and breathing · NHS: alcohol use disorder
Effects
Aggregated from 4 single-substance Erowid experience reports; 3 Erowid reports where another drug was taken too are left out
Each bar shows the share of analyzed reports whose text mentions that effect — a mention is not always a first-hand experience (fear of an effect or something witnessed can count). Mentions saying the effect did not happen are left out; that check reads keywords, so it can miss some. The shaded band on a bar, and the small range after its number, is the 95% interval: where the share could plausibly be with other reports of the same kind. Fewer reports, wider band. Tap or hover any number for details. The second value is the Bluelight extractor's per-effect confidence; a dash means the row is Erowid-derived, which has no confidence measurement.
Too few reports for bars: these effects come from 4 single-substance Erowid reports, and a bar is drawn only from 20 reports or more. With fewer, a percentage cannot tell a common effect from a rare one. Counts are shown instead. Why 20?
Effect glossary — · full glossary
Positive Effects 1
3 of 4
–
Adverse Effects 0
Also reported in combinations. In the 3 4-Fluorophenibut reports where another drug was taken too, 1 mentions hospital, emergency services or an overdose, 0 a seizure and 0 psychosis (too few reports for percentages). In the 4 single-substance reports: 0, 0 and 0. These are not in the figures above: they cannot be put down to 4-Fluorophenibut alone, and a mention is not always something that happened to the writer.
Community Trip Reports
Anecdotal first-person accounts from Reddit, Erowid, Bluelight, and Dose.wiki. Click a source to expand. Reports are harm-reduction context, not medical guidance. Tags summarise each author's own verdict — how reports are classified.
Erowid 3 reports 1 neutral 2 cautionary visit
This is a report for first-time use of a new gabaergic research chemical, F-Phenibut (CAS 52237-19-1). This is a derivative of Phenibut fluorinated at the para- or 4 position of the phenyl ring. It is very similar in structure to Baclofen, substituting a fluorine atom in the place of chlorine.
I just got a new job, but I was having a hard time being my usual relaxed, joking-around self around my coworkers for some reason. Never having used either substance before, I was doing a bit of research on Phenibut and Fluorophenibut/F-phenibut, deciding which to choose for a first time experience.
4-Fluorophenibut's nerd page
Pharmacology, chemical data, effect profiles, and more
→
Helpful Links
Import into PsychonautWiki Journal
The PsychonautWiki Journal app includes 4-Fluorophenibut, but its built-in data can be thinner than ours. Importing this file adds a separate "4-Fluorophenibut (Substance Search)" custom substance with our dose ranges and durations, so you can log against whichever you prefer. It leaves tolerance out on purpose, for the reason given under Tolerance above.
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Import this file as custom substances
and you get "4-Fluorophenibut (Substance Search)" with every
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developer.
Ranges are harm-reduction guidance, not a prescription.
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