A single dose of the anti-anxiety medication buspirone has an average elimination half-life of 2.1 hours, according to the U.S. National Library of Medicine. This elimination half-life is the time required by the human body to eliminate half the amount of a substance under natural processes.
After this period of roughly two hours, one-half of the dosage is out of the system; within four hours, one-half of the remaining buspirone is eliminated, leaving the patient with just 25% of the original dosage. The amount of buspirone left continues to decline by half every two hours, until the body is rid of the substance.
Physicians warn patients not use buspirone if they have taken an MAO inhibitor (isocarboxazid, linezolid, methylene blue injection, phenelzine, rasagiline, selegiline or tranylcypromine) within two weeks prior, as a dangerous drug interaction could result.