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Summary sheet: F-Phenibut
Molecular structure of F-Phenibut
Chemical Nomenclature
Common names F-Phenibut, Fluorophenibut, Fluorobut
Substitutive name β-(4-flourophenyl)-GABA
Systematic name 5-amino-4-(4-fluorophenyl)-1-hydroxypentan-2-one
Class Membership
Psychoactive class Depressant
Chemical class GABAergic
Routes of Administration

WARNING: Always start with lower doses due to differences between individual body weight, tolerance, metabolism, and personal sensitivity. See responsible use section.

Threshold 50 - 100 mg
Light 100 - 200 mg
Common 200 - 400 mg
Strong 400 - 600 mg
Heavy 600 mg +
Total 6 - 8 hours
Onset 20 - 60 minutes

DISCLAIMER: PW's dosage information is gathered from users and resources for educational purposes only. It is not a recommendation and should be verified with other sources for accuracy.

F-Phenibut (also known as Fluorophenibut, and Fluorobut) is a central nervous system depressant and closely related structural analog of phenibut. F-Phenibut possesses an effect profile similar to phenibut but with a faster onset, significantly increased potency, and shorter total duration.[citation needed] It has recently become available through online research chemical vendors, although little is known about this substance, particularly its potential toxicity and addiction potential.

The substance can be classified as a gabapentinoid, a class which contains other substances such as gabapentin, pregabalin [1], baclofen, and GABOB.[2][3] It is a derivative of the naturally occurring inhibitory neurotransmitter γ-aminobutyric acid (GABA), with an addition of a phenyl ring that allows it to cross the blood–brain barrier.[2]


As with phenibut, F-Phenibut is a derivative of GABA, except with a fluorine-substituted phenyl group in the β-position of the molecule. It is a chiral molecule and thus has two potential configurations as (R)- and (S)-enantiomers.[4] It has an almost identical chemical structure to baclofen (only replacing a chlorine with a fluorine atom in the para-position of the phenyl group).[5] Additionally, the widely prescribed gabapentinoid pregabalin also possesses a similar structure as phenibut, except that the phenyl group is instead replaced with an isobutyl group.


Due to the lack of research regarding the substance, all discussion regarding the pharmacology of it is purely speculation based upon its structural and subjective effect similarities to other depressants or gabapentinoid such as phenibut, gabapentin, and pregabalin.

Among other things, it is likely that this compound exerts its effects by binding to the α2δ-1 site of voltage-gated calcium channels in a manner which is similar to that of other gabapentinoids. By binding to this site, F-Phenibut may reduce the release of several excitatory neurotransmitters, including glutamate, substance P, acetylcholine, and norepinephrine. This, in turn, increases GABAergic activity.[citation needed] As the GABA system is the most prevalent inhibitory receptor set within the brain[citation needed], its modulation may be responsible for the relaxing, sedating, and calming effects of F-Phenibut on the central nervous system.

Subjective effects

The effects listed below are based upon the subjective effects index and personal experiences of PsychonautWiki contributors. The listed effects should be taken with a grain of salt and will rarely (if ever) occur all at once, but heavier doses will increase the chances and are more likely to induce a full range of effects. Likewise, adverse effects become much more likely on higher doses and may include injury or death.

In comparison to regular phenibut, this compound has a significantly faster onset, a shorter duration, and slightly less stimulation. Early reports suggest that in comparison to other commonly used GABAgenic depressants such as alcohol or benzodiazepines, this compound produces less inebriation and more euphoria, giving it more recreational potential as well as a correspondingly higher risk of abuse.

Physical effects

Cognitive effects

Experience reports

Anecdotal reports which describe the effects of this compound within our experience index include:

Additional experience reports can be found here:

Toxicity and harm potential

F-Phenibut likely has a low toxicity relative to dose. However, it is potentially lethal when mixed with depressants like alcohol, benzodiazepines or opioids.

The toxicity and long-term health effects of recreational F-Phenibut use do not seem to have been studied in any scientific context and the exact toxic dosage is unknown. This is because F-Phenibut has very little history of human usage. Anecdotal evidence from people who have tried this substance within the community suggests that there do not seem to be any negative health effects attributed to simply trying this substance at low to moderate doses by itself and using it sparingly (but nothing can be completely guaranteed).

It is strongly recommended that one use harm reduction practices when using this substance.

Tolerance and addiction potential

F-Phenibut is moderately physically and psychologically addictive, although this usually only occurs with heavy abuse of the substance. This is likely even more so than its predecessor phenibut since its more rapid onset allows more convenient compulsive redosing.

Tolerance will develop to the sedative-hypnotic effects within a couple of days of continuous use. After cessation, the tolerance returns to baseline in 7 - 14 days. Withdrawal symptoms or rebound symptoms may occur after ceasing usage abruptly following a few weeks or longer of steady dosing and may necessitate a gradual dose reduction.

Withdrawal symptoms likely include severe anxiety, nervousness, hallucinations, tremors, agitation, dizziness, tension, irritation, rapid heartbeat, fatigue, loss of appetite, nausea, vomiting, psychosis, and insomnia in a similar manner to phenibut.[6]

F-Phenibut presents cross-tolerance with all GABAgenic depressants, meaning that after its consumption most depressants will have a reduced effect.

Dangerous interactions

Although many psychoactive substances are safe on their own, they can become dangerous and even life-threatening when combined with other substances. The list below contains some common potentially dangerous combinations, but may not include all of them. Certain combinations may be safe in low doses of each but still increase the potential risk of death. Independent research should always be done to ensure that a combination of two or more substances is safe before consumption.

  • Stimulants - It can be dangerous to combine depressants with stimulants due to the risk of accidental excessive intoxication. Stimulants mask the sedative effect of depressants, which is the main factor most people use to gauge their level of intoxication. Once the stimulant effects wear off, the effects of the depressant will significantly increase, leading to intensified disinhibition, motor control loss, and dangerous black-out states. This combination can also potentially result in severe dehydration if one's fluid intake is not closely monitored. If choosing to combine these substances, one should strictly limit themselves to a pre-set schedule of dosing only a certain amount per hour until a maximum threshold has been reached.

Legal issues


This legality section is a stub.

As such, it may contain incomplete or wrong information. You can help by expanding it.

  • United Kingdom - It may be illegal to produce, supply, or import this substance under the Psychoactive Substance Act 2016, which blanketly applies the aforementioned restrictions on all "psychoactive substances" with exemptions for alcohol, nicotine and "medicinal products."[7]

See also

External links


  1. "Wyllie's Treatment of Epilepsy: Principles and Practice" | https://books.google.co.uk/books?id=j9t6Qg0kkuUC&pg=RA1-PA423&redir_esc=y#v=onepage&q&f=false
  2. 2.0 2.1 Lapin, I. (2001). "Phenibut (beta-phenyl-GABA): A tranquilizer and nootropic drug" (pdf). CNS Drug Reviews | https://doi.org/10.1111/j.1527-3458.2001.tb00211.x
  3. "Practical Management of Pain. Elsevier Health Sciences" | https://books.google.co.uk/books?id=kfcDAQAAQBAJ&pg=PA1006&redir_esc=y#v=onepage&q&f=false
  4. "Comparative pharmacological activity of optical isomers of phenibut." | https://www.ncbi.nlm.nih.gov/pubmed/18275958
  5. On neurotransmitter mechanisms of reinforcement and internal inhibition. | https://www.ncbi.nlm.nih.gov/pubmed/2431377
  6. David W. Group (25 February 2015). Encyclopedia of Mind Enhancing Foods, Drugs and Nutritional Substances, 2d ed. McFarland. pp. 186–. | https://books.google.co.uk/books?id=ZYqoBgAAQBAJ&pg=PA186&hl=en#v=onepage&q&f=false
  7. Psychoactive Substances Act 2016 (Legislation.gov.uk) | http://www.legislation.gov.uk/ukpga/2016/2/contents/enacted