Efficacy of light versus tryptophan therapy in seasonal affective disorder

Although light therapy has become the accepted treatment for patients suffering from seasonal affective disorder (SAD, winter depression), almost 40% of these patients do not respond, and require an alternative treatment.

The therapeutic effects of light versus tryptophan on SAD were studied in a repeated measures design in 13 SAD patients (11 women, 2 men). Light therapy for 2 weeks or tryptophan for 4 weeks was given, separated by a one week washout period. All were assessed with the modified Hamilton Depression Rating scale (SIGH-SAD) at the beginning and end of each treatment.

Four (31%) of the patients did not respond to either therapy. Four tryptophan-resistant patients responded to light therapy, while one light therapy-resistant patient responded to tryptophan. Relapse occurred rapidly after stopping light therapy but not after stopping tryptophan therapy.

There were significant therapeutic effects of both light (p = 0.012) and tryptophan (p = 0.014) on SAD, which were not significantly different from each other. There may be a time difference between the residual pharmacokinetic effects after stopping therapy.

The groups studied were small. This was an open study.

Tryptophan was equally effective to light therapy in treating SAD, but relapse after withdrawal of tryptophan probably occurs more slowly.