In 984 patients with generalized anxiety disorder who received buspirone in double-blind studies, the incidence of drowsiness (9 percent) did not differ significantly from that (10 percent) reported in 334 patients who received placebo. A probability value of p less than or equal to 0.10 was the criterion for significance. The incidence of drowsiness in buspirone-treated patients was significantly less than that in each of the groups receiving diazepam (32 percent), clorazepate (26 percent), lorazepam (58 percent), or alprazolam (43 percent). The side effects that did occur significantly more frequently in the buspirone group than in the placebo group were dizziness (9 percent versus 2 percent), headache (7 percent versus 2 percent), nervousness (4 percent versus 1 percent), light-headedness (4 percent versus less than 1 percent), diarrhea (3 percent versus less than 1 percent), paresthesia (2 percent versus less than 1 percent), excitation (2 percent versus less than 1 percent), and sweating/clamminess (1 percent versus 0 percent). The severities of these effects were predominantly rated as only mild or moderate. Fatigue occurred less frequently in buspirone-treated patients than in those receiving any of the benzodiazepines, and weakness occurred more frequently in diazepam-treated patients. Depression occurred less frequently in buspirone-treated patients than in those receiving clorazepate, diazepam, or lorazepam. Impotence occurred only in clorazepate- and lorazepam-treated patients. Decreased libido occurred more frequently in diazepam-treated patients, whereas increased libido was more frequent in clorazepate-treated patients. Nausea was reported more frequently in buspirone-treated patients than in those receiving clorazepate, diazepam, or alprazolam; diarrhea occurred more frequently in the buspirone group than in the diazepam group. The mean daily doses of the various treatments were buspirone, 20 mg; diazepam, 20 mg; clorazepate, 24 mg; lorazepam, 3 mg; and alprazolam, 1.5 mg. In an open-field study in West Germany involving 5,414 patients, gastrointestinal-related complaints were the most frequently reported side effects.