Prevention of primary pain is a new topic, endowed with social and economic interest. We observed that L-5-HTP can induce a significant decrease of the cropping out of migraine, the commonest primary pain. This finding seems interesting, since it represents the first data in the field and was obtained in a prospective, long-term, placebo controlled study. The result obtained suggests that CNS abnormalities underlying the mechanism of migraine can be changed by L-5-HTP, if the amino acid is administered to subjects who are predisposed to headache.