The effect of L-tryptophan on seasonal affective disorder.

Serotonin has been implicated in the etiology of seasonal affective disorder (SAD). The authors compared the effect of the serotonergic precursor L-tryptophan, placebo, and artificial evening light on 13 SAD sufferers. L-Tryptophan and light were associated with greater improvement than was placebo, but the antidepressant effects of L-tryptophan and light were not significantly different.