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Systematic (IUPAC) name
CAS number 36505-84-7
ATC code N05BE01
PubChem 2477
DrugBank APRD00222
ChemSpider 2383
Chemical data
Formula C21H31N5O2 
Mol. mass 385.50314 g/mol
Pharmacokinetic data
Bioavailability low and variable (approx. 5%), due to high first pass metabolism
Protein binding 95% bound to plasma proteins
Metabolism mainly hepatic, active metabolite 1-Pyrimidylpiperazin (1-PP)
Half life 2-3hr
Excretion urine (29-63%) and feces (18-38%) in the form of metabolites
Therapeutic considerations
Pregnancy cat.


Legal status

Rx-only, not a controlled substance

Routes oral

Buspirone (BuSpar, Ansial, Ansiced, Anxiron, Axoren, Bespar, Buspimen, Buspinol, Buspisal, Narol, Spamilan, Spitomin, Sorbon) is a psychoactive drug and member of the piperazine and azapirone chemical classes used primarily as an anxiolytic, but also to a lesser extent as an antidepressant. Bristol-Myers Squibb (BMS) gained Food and Drug Administration (FDA) approval for buspirone in 1986, and it went generic in 2001.



Comparison to Benzodiazepines

Buspirone's chemical structure and mechanism of action are completely unrelated to those of the benzodiazepines, but it purportedly has an efficacy comparable to that of diazepam (Valium) in treating GAD.[2][3] Unlike the benzodiazepines, buspirone shows no potential for addiction or dependence, and the development of tolerance has not been observed. Furthermore, cross-tolerance to benzodiazepines, barbiturates, and alcohol, as well as other GABAergics, is not present either. Additionally, it is non-sedating, non-cognitive/memory impairing, and has a generally very favorable side effect profile.

The main disadvantage of buspirone is that it may take several weeks before its anxiolytic effects become noticeable. Many patients may also require a higher dosage to adequately respond to treatment, which may also be increased in slow increments of 5 mg every three days and up to 60 mg daily, which may be the dose required for adequate relief. This makes it particularly difficult to treat patients pre-treated with benzodiazepines, for they know the immediate effects of these anxiolytics. Often patients have to be initially co-treated with a benzodiazepine for an immediate anxiolytic effect.

Therefore, benzodiazepines are often the first approach in treating anxiety disorders and panic attacks. Although buspirone may be a consideration for patients whose benzodiazepine therapy is becoming extensive beyond weeks, buspirone must not be assumed to counteract the withdrawal effects of benzodiazepines, which, in severe, chronic, and high dose cases, can include seizures, coma and death.

Benzodiazepines should be gradually withdrawn, for example alprazolam (Xanax) may safely be withdrawn by 0.25 mg every two weeks in some patients who’ve been taking large chronic doses.[citation needed] As the mechanism of action in the brain between benzodiazepines, which act as GABAA receptor positive allosteric modulators (PAMs), and buspirone, which acts as a serotonin receptor agonist is uncorrelated, it is essential that buspirone is not considered an anxiolytic agent which may shorten the benzodiazepine withdrawal syndrome or help prevent or lessen the severity of benzodiazepine withdrawal symptoms.


Buspirone functions as a serotonin 5-HT1A receptor partial agonist.[4] It is this action that is thought to mediate its anxiolytic and antidepressant effects. Additionally, it functions as a dopamine D2, α1, and α2-adrenergic receptor antagonist to a lesser degree, though these properties are generally undesirable in an anxiolytic and likely only contribute to side effects.


The action of a single dose of buspirone is much longer than its short half-life of 2–3 hours actually indicates.[citation needed] Buspirone's bioavailability is very low and variable due to extensive first-pass metabolism, it's quickly absorbed, and it's highly plasma bound (95%). Taking it together with food may significantly increase its bioavailability. Buspirone's active metabolite 1-pyrimidinylpiperazine (1-PP) is also a 5-HT1A partial agonist with anxiolytic properties, but weaker so than the parent compound. It may account for bupsirone's extended duration of action.

Side Effects

Buspirone's side effects may include:

Other side effects have been reported, but are not more frequent than those encountered with placebo. An unusual side effect reported by patients is an enhanced sense of smell.

Rarely, buspirone's may have a dangerous nature or intensity. Some tend to disappear with continued therapy, or are less frequent if the initial dose is low and increased gradually.



Abuse and Dependence

Buspirone has no known potential for abuse or psychological or physiological dependence.[6]


  1. Kline, Anthony, E., Olsen, Adam, S., Zafonte, Ross D., Sozda, Christopher N., Aslam, Haris, A., and Cheng, Jeffrey P. (September 2007). "Brain injury delayed and chronic buspirone treatment after experimental traumatic brain injury enhances spatial acquisition". Archives of Physical Medicine and Rehabilitation. 88 (9): E6.
  2. Cohn, JB; Rickels K (1989). "A pooled, double-blind comparison of the effects of buspirone, diazepam and placebo in women with chronic anxiety". Curr Med Res Opin. 11 (5): 304–320. 
  3. Goldberg, HL; Finnerty RJ (September 1979). "The comparative efficacy of buspirone and diazepam in the treatment of anxiety". Am J Psychiatry 136 (9): 1184–1187. 
  4. Bller P (May 1997). "'Selective activation of postsynaptic 5-HT1A receptors induces rapid antidepressant response.'". Neuropsychopharmacology (5). 
  5. Lilja, JJ; Kivisto KT, Backman JT, Lamberg TS, Neuvonen PJ (December 1998). "Grapefruit juice substantially increases plasma concentrations of buspirone". Clinical Pharmacology & Therapeutics 64 (6): 655–660. doi:10.1016/S0009-9236(98)90056-X. 
  6. Lydiurd, R. Bruce (2000). "An Overview of Generalized Anxiety Disorder: Disease State-Appropriate Therapy". Clinical Therapeutics 22 (Supplement A): A3–A24. doi:10.1016/S0149-2918(00)89070-0. 


Up to date as of January 15, 2010

Definition from Wiktionary, a free dictionary





buspirone (uncountable)

Wikipedia has an article on:


  1. An anxiolytic agent and serotonin receptor agonist of the azaspirodecanedione class of compounds.

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