How Long Does Buspar (Buspirone) Last?

In our latest question and answer, the pharmacist discusses how long Buspar (buspirone) lasts in the body.

Jan 26, 2018

Sweetie asked

I had taken 5mg buspirone at 6:30pm, and then at around 10:30pm. I took a natural melatonin tab that contains 30mg 5HTP, should I be worried about an interaction or serotonin syndrome?


Buspar (buspirone) is an anti-anxiety medication that is both structurally and pharmacologically different from other classes of anxiolytics such as benzodiazepines (e.g. Valium). Buspar (buspirone) is commonly used for mild to moderate cases of anxiety and typically does not cause physical dependence and doesn't significantly affect cognition or motor function. 

While Buspar (buspirone) is generally considered a safer medication to use for symptoms of anxiety when compared to other classes of drugs, it does not confer immediate relief and effects can take up to two weeks to take place. More commonly, it takes around 3 to 6 weeks for full effects to take place.

How Long Does Buspar (Buspirone) Last?

When taken by mouth, Buspar (buspirone) is quickly absorbed and the onset of action is generally 30 minutes to one hour. Once taken consistently, the effects of each dose last around 8 to 12 hours. Thus, for most individuals, it is commonly dosed two to three times daily to retain effect.

In terms of metabolism, Buspar (buspirone) has a short half life (time it takes for 50% of the drug to be metabolized) of around 2 to 4 hours. Taking Buspar (buspirone) with food may prolong the effects of the drug. Studies have shown that the maximum concentrations of the drug are increased over 100% when administered with food. In addition, food may reduce the clearance of Buspar (buspirone).  

It is generally accepted that it takes about 5 half lives for a drug to be considered completely metabolized and eliminated from the body. Therefore, you can expect Buspar (buspirone) to be completely metabolized after about 10-20 hours.

Lastly, there are no reports of serotonin syndrome caused by Buspar (buspirone) and supplementation with 5-HTP (serotonin). However, Buspar (buspirone) is known to affect serotonin levels and when taken consistently, there may be a net overall increase in the neurotransmitter which may be relatively independent of the drug's half life. In order words, the effects on serotonin may last longer than the drug is present in the body.

There have been anecdotal reports of serotonin syndrome in those combining Buspar and St. Johns Wort, a commonly used herbal product for depression.  It is unknown what the risk would be of combining Buspar and products that increase or contain serotonin. If you do choose to use them together, be sure to let your doctor know.

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