5-Hydroxytryptamine-2 antagonist increases human slow wave sleep.

Ritanserin, a specific 5-HT2 antagonist, was given to volunteers in a double-blind placebo controlled sleep study. Slow wave sleep doubled in duration at the expense of stage 2. The finding that a serotonin antagonist changed the architecture of sleep without producing insomnia is of fundamental importance and calls for a re-examination of traditional theories of sleep control which assign a facilitatory role to serotonin.