L-tryptophan augmentation of light therapy in patients with seasonal affective disorder

Can J Psychiatry. 1997 Apr;42(3):303-6. doi: 10.1177/070674379704200309.


Objective: Up to one-third of patients with seasonal affective disorder (SAD) do not have a full response to light therapy. Given the evidence for serotonergic dysregulation in SAD, we examined the possible role of l-tryptophan as an augmentation strategy for nonresponders and partial responders to light therapy.

Method: Eligible drug-free patients meeting DSM-IV criteria for SAD were treated for 2 weeks using a standard morning light therapy regimen (10,000 lux cool-white fluorescent light for 30 minutes). Partial and nonresponders were treated for 2 weeks with open-label l-tryptophan (1 g 3 times daily) while light therapy was continued. Ratings at baseline and follow-up included the 29-item Structured Interview Guide for the Hamilton Depression Rating Scale, SAD version (SIGH-SAD) and the Clinical Global Impression (CGI) scale.

Results: Sixteen patients began the l-tryptophan augmentation phase. Two patients discontinued medications within 3 days because of side effects. In the 14 patients completing treatment, the addition of l-tryptophan resulted in significant reduction of mean depression scores. Nine of 14 patients (64%) showed very good clinical responses to combined treatment and minimal side effects.

Conclusion: This open-label study suggests that l-tryptophan may be an effective augmentation strategy for those patients with SAD who show limited or poor response to bright ligh therapy. Further placebo-controlled studies are warranted to demonstrate efficacy.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Combined Modality Therapy
  • Dose-Response Relationship, Drug
  • Drug Administration Schedule
  • Female
  • Humans
  • Male
  • Middle Aged
  • Personality Inventory
  • Phototherapy*
  • Seasonal Affective Disorder / diagnosis
  • Seasonal Affective Disorder / psychology
  • Seasonal Affective Disorder / therapy*
  • Treatment Outcome
  • Tryptophan / administration & dosage*


  • Tryptophan