Evidence for serotonin-S2 receptor involvement in analgesia in humans.

The possible analgesic activity of ritanserin (a new very selective and potent serotonin-S2 antagonist) was studied (double-blind) in humans. A significant increase in nociceptive flexion reflex threshold and subjective pain threshold was observed after five days of treatment, while treatment with placebo did not induce any change. The effects of ritanserin were not reversed by either naloxone or saline (double-blind) administration. Our data suggest a possible role of serotonin-S2 receptors in analgesia.