|This article relies too much on references to primary sources. (January 2015)|
|Systematic (IUPAC) name|
|Biological half-life||5.3 hours (after 250 mg dose)|
|Synonyms||Fenibut, Fenigam, Phenigam, Phenybut, Phenygam, Phenylgamma, PHG, PhGABA|
|Molar mass||179.216 g/mol|
|Melting point||253 °C (487 °F)|
|(what is this?)|
Phenibut (or, alternatively, fenibut, phenybut) (brand name Noofen, Citrocard), contracted from β-phenyl-γ-aminobutyric acid (β-phenyl-GABA), is a central depressant and derivative of the naturally occurring inhibitory neurotransmitter γ-aminobutyric acid (GABA), or a GABA analogue. The addition of a phenyl ring allows phenibut to cross the blood–brain barrier. Phenibut was developed in the Soviet Union in the 1960s, and has since been used there as a pharmaceutical drug to treat a wide range of ailments, including posttraumatic stress disorder, anxiety, depression, asthenia, insomnia, alcoholism, stuttering, and vestibular disorders, among other conditions. In some other parts of the world, phenibut is not approved for clinical use, and is instead sold as a nutritional supplement. It has been reported by some researchers to possess nootropic actions for its ability to improve neurological functions,[medical citation needed] but others have not observed these effects. It is generally accepted that phenibut has anxiolytic effects in both animal models and in humans.
Phenibut is a close structural analogue of GABA, as well as of baclofen (β-(4-chlorophenyl)-GABA), pregabalin (β-isobutyl-GABA), and GABOB (β-hydroxy-GABA). Originally thought to act as a selective GABAB receptor agonist, phenibut has since been found to act preferentially as a blocker of α2δ subunit-containing voltage-gated calcium channels, similarly to gabapentin and pregabalin. As such, by definition, phenibut is a gabapentinoid.
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.
In terms of chemical structure, phenibut is a derivative of GABA with a phenyl group in the β-position. It is a chiral molecule and thus has two potential configurations, an (R)- and (S)-enantiomer. It has almost the same structure of baclofen (lacking only a chlorine atom in the para-position of the phenyl group) and contains phenethylamine in its structure. Pregabalin has the same structure as phenibut except that the phenyl group is instead an isobutyl group.
Phenibut hydrochloride 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 acts as an agonist of the GABAB receptor (specifically, a full agonist), similarly to baclofen and γ-hydroxybutyric acid (GHB), and at higher doses also of the GABAA receptor. It has some 30- to 68-fold lower affinity for the GABAB receptor relative to baclofen, which is active at far lower doses in comparison. There is dispute in the literature about whether or not phenibut binds to the GABAA receptor, which is the receptor responsible for the actions of the benzodiazepines, barbiturates, and Z-drugs, and for the main effects of ethanol. According to Allikmets and Ryage (1983) and Shulgina (1986), phenibut does bind to the GABAA receptor, but according to Lapin (2001), it does not. In the case of the former, it is argued that the GABAA binding only occurs at higher concentrations.
The literature that supports the nootropic effects of phenibut also suggest that it elicits tranquilizing effects, 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, though studies on other GABAB agonists, such as GHB and the phenibut analogue baclofen, have shown them to act as potential convulsants. It should be noted, however, that GHB acts on the convulsion-inducing GHB receptor, which phenibut does not. Phenibut has been found to reduce immobility time in the forced swim test, a measure of possible antidepressant activity, which was blocked by a GABAB receptor antagonist. It has been found to increase dopamine levels in the striatum, and it was suggested that phenibut may activate dopaminergic processes and that this may be involved in its effects. Anecdotal evidence indicates that phenibut can produce euphoria. Recreational use of the drug has been reported. In Europe, phenibut has been mentioned as a "novel psychoactive substance", although it is produced and prescribed in an EU member Latvia, with its producer Olainfarm recently receiving EU funding for expanding facilities used for phenibut's intermediate product production.
Subsequent research has found that phenibut also binds to and potently blocks α2δ subunit-containing voltage-gated calcium channels (VGCCs), similarly to gabapentin and pregabalin. Both enantiomers of phenibut show this action with similar efficacy. Moreover, the R-enantiomer possesses five-fold greater affinity for this site relative to the GABAB receptor, while the S-enantiomer does not bind to the GABAB receptor at all. As such, phenibut is likely to have much greater effect on α2δ subunit-containing VGCCs than on the GABAB receptor. Notably, the antinociceptive effects of phenibut in rodents are mediated not by the GABAB receptor but by blockade of α2δ subunit-containing VGCCs.
For medical use, phenibut is generally prescribed at a dosage of 250–1500 mg twice a day.
The side effects of phenibut are said to be similar to but milder than those of baclofen. They include sleepiness and hangover-like effects such as headache and depression once the drug has worn off.
Limited evidence indicates that withdrawal symptoms of phenibut include severe anxiety, nervousness, tremors, agitation, dizziness, irritation, fatigue, loss of appetite, rapid heartbeat, nausea, vomiting, tension, psychosis, hallucinations, and insomnia. These symptoms may last as long as two weeks. Tolerance to phenibut may develop rapidly with repeated use.
Phenibut should not be combined with alcohol, sedatives, monoamine oxidase inhibitors, anticonvulsants like carbamazepine, or other prescription drugs. Persons on such medications should consult with their medical practitioners prior to taking phenibut. Evidence suggests that phenibut can modulate the function of some epilepsy medications.
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