Fluorophenibut Review: Benefits, Dosage, Side Effects & Phenibut Comparison
Fluorophenibut (F-phenibut) is a fluorinated relative of phenibut that activates GABA-B receptors. It attracts interest for relaxation, sociability, and sleep. Laboratory research shows that it suppresses electrical firing in mouse Purkinje cells, while human case reports describe intoxication and withdrawal. [1] [2]
This review covers F-phenibut vs. Phenibut, the potency study, FAA and HCl forms, and reported side effects. The related product featured below is Phenibut, not Fluorophenibut.
What Is Fluorophenibut?
Fluorophenibut is a synthetic GABA analog also called F-phenibut, 4F-phenibut, 4-fluorophenibut, or CGP 11130. Its structure contains a fluorine atom at the para position of the phenyl ring. The chemical identifiers below describe the parent compound, rather than its hydrochloride salt.
| Identifier | Fluorophenibut |
|---|---|
| Common names | F-phenibut; 4F-phenibut; 4-fluorophenibut |
| Development code | CGP 11130 |
| Molecular formula | C10H12FNO2 |
| Molecular weight | 197.21 g/mol |
| CAS number | 52237-19-1 |
| PubChem CID | 103611 |
| IUPAC name | 4-amino-3-(4-fluorophenyl)butanoic acid |
| InChIKey | QWHXHLDNSXLAPX-UHFFFAOYSA-N |
Phenibut has a history of medical use for anxiety and insomnia in Russia and other countries. Fluorophenibut is its para-fluorinated analog. Our Phenibut review covers the parent compound separately. [3]
The fluorophenyl group is the fluorine-substituted ring within the molecule. Fluorophenibut also contains an amino group and a carboxylic-acid chain. Its CAS number, 52237-19-1, identifies the complete parent compound in chemical databases and research catalogs.
Fluorophenibut Benefits: Reported Relaxation and Sleep Effects
User reports describe calmness, easier social interaction, and sedation. The human sources reviewed here consist of individual experiences and clinical case reports. A ClinicalTrials.gov search returned no registered fluorophenibut studies on November 7, 2026. [4]
Anxiety Relief and Sociability
Some users describe less social inhibition and a relaxed mood. The June 2022 discussion examined below includes an account of sociability and motivation to draw.
Sleep and Sedation
Some accounts emphasize sedation more than sociability. One commenter in the same discussion preferred regular phenibut and described F-phenibut as more sedating. The March 2025 report discussed below describes insomnia after twelve days of daily use.
How Does Fluorophenibut Work?
Fluorophenibut activates GABA-B receptors, which participate in inhibitory signaling. Irie and colleagues studied its effects in cerebellar slices from young male and female mice using patch-clamp recordings. This method measures electrical activity directly in individual cells.
In Purkinje cells, F-phenibut activated an outward-rectifying potassium current and suppressed action-potential generation. The investigators compared three compounds using the same electrical endpoint. Their EC50 values describe the concentration producing half of the maximal current response, measured in micromoles per liter.
| Compound | Current-response EC50 |
|---|---|
| Phenibut | 1,362 ÂĩM |
| F-phenibut | 23.3 ÂĩM |
| Baclofen | 6.0 ÂĩM |
In this mouse-cell assay, F-phenibut reached the half-maximal current response at approximately 58 times lower concentration than phenibut, calculated as 1,362 divided by 23.3. Baclofen required approximately 3.9 times lower concentration than F-phenibut. The potency order for this endpoint was baclofen, F-phenibut, then phenibut. [2]
F-Phenibut vs. Phenibut: Effects and Tolerance
F-phenibut and phenibut share related chemistry and GABA-B activity. The fluorine substitution changes the molecule and its activity in the Purkinje-cell experiment.
| Question | Phenibut | F-phenibut |
|---|---|---|
| Chemical difference | Unsubstituted phenyl ring | Fluorine substitution on the phenyl ring |
| Research history | Medical-use literature and substantial toxicity reporting | Direct receptor/cell experiments and limited human case reports |
| Studied targets | R-phenibut binds the alpha-2-delta calcium-channel subunit | GABA-B activity measured in mouse Purkinje cells |
| Repeated use | Dependence and withdrawal are documented | Withdrawal reported in clinical cases |
In a 2015 study, R-phenibut bound the alpha-2-delta subunit of voltage-dependent calcium channels and produced antinociceptive effects in animal models. The alpha-2-delta subunit is also a binding target of gabapentin, giving R-phenibut a second studied pharmacological action alongside GABA-B activation. [5]
Users sometimes describe F-phenibut as faster acting, shorter lasting, or more sedating than phenibut. Preferences vary: the Reddit discussion below includes both an enthusiastic initial account and a commenter who preferred the parent compound.
Fluorophenibut Dosage, Half-Life and Forms
There is no validated human fluorophenibut dosage regimen. Online milligram ranges come largely from self-experimentation and vendor descriptions.
Fluorophenibut Half-Life and Duration
A measured human half-life for fluorophenibut has not been established. Half-life describes the time it takes a substance's concentration to fall by half during elimination. User descriptions of onset and duration instead concern when the effects become noticeable and how long they feel them.
Fluorophenibut FAA vs. HCl
FAA means free amino acid; HCl identifies the hydrochloride salt. The parent compound has a molecular weight of 197.21 g/mol. The hydrochloride reference standard has formula C10H12FNO2¡HCl, formula weight 233.7 g/mol, and CAS number 1858241-03-8. [6]
The hydrochloride salt has a higher formula weight because it includes HCl. The FAA label also appears on Phenibut FAA products, which contain the unfluorinated compound.
Fluorophenibut Side Effects and Safety
Published human reports describe severe sedation, agitation, and withdrawal symptoms. The cases below identify the substances involved, symptoms, treatment, and course of recovery.
Reported Intoxication
A 2022 toxicology abstract described a 34-year-old man who took 4-fluorophenibut and fladrafinil. He developed alternating agitation and stupor with seizure-like movements and required intubation. Continuous EEG showed severe diffuse encephalopathy without recorded seizures; his mental status returned to baseline 120 hours after admission. The amount taken was unknown. [7]
Tolerance and Withdrawal
Tolerance means that an effect becomes weaker with repeated exposure. Physical dependence concerns adaptation that produces symptoms when use is reduced or stopped.
A 2024 conference poster described a 23-year-old man with anxiety, paranoia, and insomnia after stopping months of daily F-phenibut use. He had previously used kratom and stopped it about a month earlier. Hospital treatment included baclofen and gabapentin, with improvement during admission. [8]
A separate 2022 report involved combined 4-fluorophenibut and bromazolam withdrawal, with prolonged intensive care and serious complications. Laboratory analysis identified both substances in the supplied materials. [9]
If someone becomes difficult to wake, has breathing trouble, seizures, or severe confusion after exposure, seek emergency medical care. Regular users developing symptoms between doses should seek medical advice before abruptly stopping. Bring the product label and a clear account of other substances used.
Fluorophenibut Reddit Experiences
Two original Reddit discussions capture contrasting experiences: an initially positive account of sociability and a report of anxiety and poor sleep after repeated use.
Relaxation and the Urge to Redose
In a June 2022 r/researchchemicals thread, u/ICBM-in-pill-form described a pleasant buzz, sociability, and motivation to draw, followed by an urge to take more. The account also involved cannabis and several other sedating substances. A later edit reported a much weaker effect on another occasion.
Commenter u/g0neunder described F-phenibut as faster, shorter, and more sedating than regular phenibut, while preferring phenibut overall. [10]
Anxiety and Poor Sleep After Repeated Use
In March 2025, u/dumbdumbpoopoo reported anxiety, restlessness, insomnia, reduced appetite, and a fast heartbeat after twelve days of daily fluorophenibut use. The author described the experience as withdrawal or rebound and asked for help. [11]
Where to Buy F-Phenibut
The product below is Phenibut HCl powder, 50 grams, the related unfluorinated compound. Its product page provides the current packaging, price, and research-use information.
Fluorophenibut Review: Conclusion
Fluorophenibut activates GABA-B-mediated signaling and is substantially more potent than phenibut in the published Purkinje-cell experiment. User reports explain its appeal for relaxation and sociability, while clinical reports document serious intoxication and withdrawal.
Fluorophenibut FAQs
These questions cover drug screening, neuroprotection, serotonin, pregnancy, and FDA status.
Will Fluorophenibut Show Up on a Routine Drug Test?
Fluorophenibut was not detected on the routine urine drug screen reported in the 2024 withdrawal case. In the 2022 mixed-withdrawal report, laboratory analysis identified 4-fluorophenibut in supplied material. That analysis also identified bromazolam in the other supplied product.
Is Fluorophenibut Neuroprotective?
Fluorophenibut has no demonstrated neuroprotective benefit in humans. The related R-phenibut study used a rat model of focal cerebral ischemia, in which blood flow to part of the brain was restricted. Researchers assessed its neuroprotective effects after that experimental injury.
Does Fluorophenibut Increase Serotonin?
An increase in serotonin has not been demonstrated for fluorophenibut in humans. Serotonin is a different signaling molecule from GABA. The direct F-phenibut experiment examined GABA-B-related electrical responses in Purkinje cells.
Is Fluorophenibut Safe During Pregnancy?
Fluorophenibut's safety during pregnancy is unknown. Anyone pregnant or breastfeeding who has used it should discuss the exposure and any ongoing use with their clinician. The product name, amount, timing, and other substances used will help that assessment.
Does Fluorophenibut Have FDA Approval?
Fluorophenibut is not an FDA-approved medicine. Its substance-database entry assigns the identifier UNII 6DAU7M5P3D for chemical identification. Separately, FDA guidance excludes the parent compound phenibut from the definition of a dietary ingredient.
Sources for the FAQs: the F-phenibut clinical reports above; the R-phenibut stroke experiment [12]; the FDA substance record [13]; and FDA dietary-ingredient guidance [14].
- PubChem. "4-Fluorophenibut, CID 103611." Chemical identifiers. Accessed November 7, 2026. â
- Irie T, Yamazaki D, Kikura-Hanajiri R. "F-phenibut, a potent GABA-B receptor agonist, activates an outward-rectifying potassium current and suppresses action potentials in mouse cerebellar Purkinje cells." European Journal of Pharmacology. 2020;884:173437. â â
- World Health Organization. "Phenibut: Critical Review Report." 44th Expert Committee on Drug Dependence. 2021. â
- ClinicalTrials.gov. "Search for fluorophenibut or F-phenibut." No registered studies returned in our November 7, 2026 search. â
- Zvejniece L, et al.. "R-phenibut binds to the alpha-2-delta subunit of voltage-dependent calcium channels and exerts gabapentin-like anti-nociceptive effects." Pharmacology Biochemistry and Behavior. 2015;137:23-29. â
- Cayman Chemical. "4-fluoro Phenibut (hydrochloride), item 30232." Analytical reference standard: identity and technical information. Accessed November 7, 2026. â
- Adkins A, Gramm E, Shulman J, Pizon A. "BaFLofen: a case of nootropics gone awry leading to 4-fluorophenibut toxicity." Clinical Toxicology. 2022;60(Suppl 2):87. NACCT abstract 176. â
- Kain K II, Glenn J, Koefed A. "Case report: management of F-phenibut withdrawal." Royal College of Psychiatrists International Congress. 2024. Poster P-808. â
- Chen K, Chamberlin L, Borg D, Davenport M, Stripp M. "Acute severe withdrawal associated with 4-fluorophenibut and bromazolam exposure." Clinical Toxicology. 2022;60(Suppl 2):14. NACCT abstract 27. â
- u/ICBM-in-pill-form and commenters. "F-Phenibut/F-Phen/4-Fluorophenibut: experience discussion." Reddit, r/researchchemicals. June 2022. Individual experiences. â
- u/dumbdumbpoopoo. "Warning about fluorophenibut: withdrawal or rebound after 12 days." Reddit, r/quittingphenibut. March 28, 2025. Individual experience. â
- Vavers E, et al.. "The neuroprotective effects of R-phenibut after focal cerebral ischemia." Pharmacological Research. 2016;113(Pt B):796-801. â
- U.S. Food and Drug Administration. "4-Fluorophenibut, UNII 6DAU7M5P3D." Substance Registration System. UNII availability does not imply regulatory review or approval. â
- U.S. Food and Drug Administration. "Phenibut in dietary supplements." Regulatory information. Accessed November 7, 2026. â