The effects of trazodone on sleep were compared with those of placebo and the sedating tricyclic antidepressant trimipramine in a double-blind crossover study in six healthy young men. Only trazodone significantly increased deep sleep without otherwise altering the normal architecture of sleep. The alpha-adrenergic receptor-blocking property of trazodone and a relative lack of noradrenergic reuptake blocking and the lack of anticholinergic effects are hypothesized to be responsible for the effects on sleep.