Efficacy of light versus tryptophan therapy in seasonal affective disorder

J Affect Disord. 1998 Jul;50(1):23-7. doi: 10.1016/s0165-0327(98)00053-6.


Background: 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.

Methods: 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.

Results: 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.

Conclusions: 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.

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

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

Publication types

  • Clinical Trial
  • Randomized Controlled Trial

MeSH terms

  • Adult
  • Antidepressive Agents / therapeutic use*
  • Cross-Over Studies
  • Female
  • Humans
  • Male
  • Phototherapy*
  • Seasonal Affective Disorder / drug therapy
  • Seasonal Affective Disorder / therapy*
  • Tryptophan / therapeutic use*


  • Antidepressive Agents
  • Tryptophan