The effect of treatment with astemizole for three weeks on weight was assessed in 44 patients with seasonal allergic rhinitis who participated in a randomized, double-blind, placebo-controlled clinical trial. Astemizole 10-mg tablets and identical placebo tablets were used. Compared with baseline, weight increased significantly in astemizole-treated patients (1.07 +/- 1.39 kg; p = 0.0004); however, the mean change in weight in astemizole-treated patients was not statistically significantly different than that seen in placebo-treated patients (0.85 +/- 1.68 kg). No relationship was found between changes in weight and age, sex, initial weight, percentage of obesity, and plasma astemizole concentrations.