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Phenibut skeletal formula.svg
Phenibut ball-and-stick model.png
Systematic (IUPAC) name
(RS)-4-amino-3-phenyl-butyric acid
Clinical data
Trade names Noofen
Legal status
  • US: Not FDA approved
Routes of
Pharmacokinetic data
Biological half-life 5 hours
CAS Registry Number 1078-21-3 N
ATC code N06BX22
PubChem CID: 14113
ChemSpider 13491 YesY
Synonyms Fenibut, Fenigam, Phenigam, Phenybut, Phenygam, Phenylgamma, PHG, PhGABA[1]
Chemical data
Formula C10H13NO2
Molecular mass 179.216 g/mol
Physical data
Melting point 253 °C (487 °F)
 N (what is this?)  (verify)

Phenibut[note 1], contracted from β-phenyl-γ-aminobutyric acid (β-phenyl-GABA), is a central nervous system (CNS) depressant and derivative of the naturally occurring inhibitory neurotransmitter γ-aminobutyric acid (GABA). The addition of a phenyl ring allows phenibut to cross the blood–brain barrier.[2] Phenibut is sold as a nutritional supplement,[3] and is not approved as a pharmaceutical in the United States or Europe, but in Russia it is sold as a psychotropic drug. It has been reported by some to possess nootropic actions for its ability to improve neurological functions,[4][medical citation needed] but other researchers have not observed these effects.[5] It is generally accepted that phenibut has anxiolytic effects in both animal models and in humans.[2] Phenibut was discovered in the Soviet Union in the 1960s, and has since been used there to treat a wide range of ailments including posttraumatic stress disorder, anxiety, and insomnia.[4]

Phenibut is a close structural analogue of GABA, as well as of GABOB (β-hydroxy-GABA), baclofen (β-(4-chlorophenyl)-GABA), and pregabalin (β-isobutyl-GABA).[6]


Phenibut was synthesized at the A. I. Herzen Leningrad Pedagogical Institute (USSR) by Professor Vsevolod Perekalin's team and tested at the Institute of Experimental Medicine, USSR Academy of Medical Sciences.

Phenibut is mandated standard equipment in a Russian cosmonaut's medical kit. The use of "conventional" tranquilizers for stress and anxiety makes patients drowsy, which was deemed unacceptable for cosmonauts; phenibut, however, lowers stress levels without adversely affecting performance.[medical citation needed] In 1975 phenibut was included in the cosmonauts' kit for those who participated in the Apollo-Soyuz joint mission.[7]

General information[edit]

In chemical structure, phenibut is a phenyl derivative of GABA. Although the calming action is similar to other GABA agonists,[medical citation needed] phenibut binds to the GABAB metabotropic receptor, the same site responsible for the sedative effects of baclofen (the para-chloro derivative of phenibut) and γ-hydroxybutyrate (GHB), although GHB also acts at the GHB receptor.[8] There is dispute in the literature about whether or not phenibut binds to the GABAA ionotropic receptor, which is responsible for the actions of the benzodiazepines, barbiturates, and Z-drugs, and for some of the effects of ethanol. According to Allikmets and Ryage (1983) and Shulgina (1986) phenibut does bind to the GABAA receptor,[4] but according to Lapin (2001) it does not.[2] In the case of the former, it is argued that the GABAA binding only occurs at higher concentrations.[4]

The literature that supports the nootropic effects of phenibut also suggest it elicits tranquilizing effects,[2] reduction of stress and anxiety, improvement of impaired sleep, and the potentiation (enhancement) of the effects of tranquilizers, narcotics, and neuroleptics. It is also suggested to have an anticonvulsant effect,[4] though studies on other GABAB agonists, such as GHB and the phenibut analogue baclofen, have shown them to act as potential convulsants.[citation needed] It should be noted, however, that GHB acts on the convulsion-inducing GHB receptor,[9] which phenibut does not.

Physical properties[edit]

Phenibut HCl is a white crystalline powder and the taste is very sour. It is readily soluble in water and in alcohol, and the pH of a 2.5% water solution is about 2.3–2.7.


Phenibut is a γ-aminobutyric acid with a phenyl group in the β-position. It is a chiral molecule and thus has two potential configurations, an (R)- and (S)-enantiomer. In phenibut, only the (R)-enantiomer is biologically active leaving the (S)-enantiomer of little value.[8] It has the same structure of baclofen[4] (lacking only a chlorine atom in the para-position of the phenyl group) and includes the phenylethylamine structure.
Pregabalin has instead the phenyl group substituted with the isobutyl group.


Phenibut acts as an agonist of the GABAB receptor, similarly to baclofen and γ-hydroxybutyric acid (GHB), and at higher doses also of the GABAA receptor.[4][10]

Recently, it has been found that phenibut binds to the α2δ subunit of voltage-gated calcium channels (VGCCs), with the R-enantiomer possessing five-fold greater affinity for this site relative to the GABAB receptor (the S-enantiomer does not bind to the GABAB receptor), and phenibut inhibits these channels similarly to gabapentin and pregabalin.[11] Moreover, it has been found that the antinociceptive effects of phenibut in rodents are mediated not by the GABAB receptor but by blockade of α2δ subunit-containing VGCCs, implicating this action as an important mediator of a significant portion of the effects of phenibut.[11]

Contraindications and side effects[edit]

Persons on MAO inhibitors or epilepsy medications like carbamazepine or oxcarbazepine should consult with their physician or pharmacist prior to supplementation with phenibut. Some evidence suggests that phenibut can modulate the function of some epilepsy medications.[4]

See also[edit]


  1. ^ J. Elks (14 November 2014). The Dictionary of Drugs: Chemical Data: Chemical Data, Structures and Bibliographies. Springer. pp. 69–. ISBN 978-1-4757-2085-3. 
  2. ^ a b c d Lapin, I. (2001). "Phenibut (beta-phenyl-GABA): A tranquilizer and nootropic drug" (pdf). CNS Drug Reviews 7 (4): 471–481. doi:10.1111/j.1527-3458.2001.tb00211.x. PMID 11830761. 
  3. ^ Nelson, LS (2008). "Phenibut Withdrawal - A Novel 'Nutritional Supplement'". Clinical Toxicology 46 (7): 605. doi:10.1080/15563650802255033. 
  4. ^ a b c d e f g h Shulgina, G. I. (1986). "On neurotransmitter mechanisms of reinforcement and internal inhibition". The Pavlovian journal of biological science 21 (4): 129–140. doi:10.1007/BF02734511. ISSN 0093-2213. PMID 2431377. 
  5. ^ Kovaleva, E. L. (1984). "Comparative characteristics of the nootropic action of fenibut and fepiron". Farmakologiia i toksikologiia 47 (1): 20–23. PMID 6705902. 
  6. ^ Lapin I (2001). "Phenibut (beta-phenyl-GABA): a tranquilizer and nootropic drug". CNS Drug Rev 7 (4): 471–81. PMID 11830761. 
  7. ^ Slava Lapin (30 July 2009). From the Inside. Luniver Press. p. 209. ISBN 978-1-905986-11-8. Retrieved 6 November 2010. 
  8. ^ a b Dambrova, M.; Zvejniece, L.; Liepinsh, E.; Cirule, H.; Zharkova, O.; Veinberg, G.; Kalvinsh, I. (2008). "Comparative pharmacological activity of optical isomers of phenibut". European Journal of Pharmacology 583 (1): 128–134. doi:10.1016/j.ejphar.2008.01.015. PMID 18275958. 
  9. ^ Banerjee, P. K.; Snead Oc, 3. (1995). "Presynaptic gamma-hydroxybutyric acid (GHB) and gamma-aminobutyric acidB (GABAB) receptor-mediated release of GABA and glutamate (GLU) in rat thalamic ventrobasal nucleus (VB): A possible mechanism for the generation of absence-like seizures induced by GHB". The Journal of Pharmacology and Experimental Therapeutics 273 (3): 1534–1543. PMID 7791129. 
  10. ^ Zyablitseva, Evgeniya A.; Kositsyn, Nikolay S.; Shul'gina, Galina I. (2013). "The Effects of Agonists of Ionotropic GABAA and Metabotropic GABAB Receptors on Learning". The Spanish journal of psychology 12 (01): 12–20. doi:10.1017/S1138741600001438. ISSN 1138-7416. 
  11. ^ a b Zvejniece, Liga; Vavers, Edijs; Svalbe, Baiba; Veinberg, Grigory; Rizhanova, Kristina; Liepins, Vilnis; Kalvinsh, Ivars; Dambrova, Maija (2015). "R-phenibut binds to the α2–δ subunit of voltage-dependent calcium channels and exerts gabapentin-like anti-nociceptive effects". Pharmacology Biochemistry and Behavior 137: 23–29. doi:10.1016/j.pbb.2015.07.014. ISSN 0091-3057. 


  1. ^ Synonyms and alternate spellings include: fenibut, phenybut and Noofen.

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