Recent systematic review s have shown that  light therapy  is an efficacious and well-tolerated treatment for SAD .
There is also evidence for efficacy of pharmacotherapy to treat and prevent SAD .
SAD is a common condition with significant psychosocial impairment .
BACKGROUND Seasonal affective disorder ( SAD ) consists of recurrent major depressive episodes in the fall/winter with remissions in spring/summer .
RESULTS A careful history is important to make the diagnosis and differentiate SAD from other similar conditions such as subsyndromal SAD and atypical depression .
Seasonal patterns with winter worsening are also recognized in " nonseasonal " depression as well as many other psychiatric conditions , and comorbidity with SAD is common .
The pathophysiology of SAD seems to be heterogeneous as research on circadian , neurotransmitter function and genetic hypotheses have shown discrepant results .
A dual vulnerability model with differential loading on separate seasonal and depression factors has been proposed to explain these findings .
Effects of rapid tryptophan depletion in patients with seasonal affective disorder in remission after light therapy.
BACKGROUND Previous studies show that rapid tryptophan depletion reverses the effects of therapy with serotonergic , but not noradrenergic , antidepressant drugs in patients with remitted nonseasonal depression . The objective of this study was to investigate the effects of rapid tryptophan depletion in patients with seasonal affective disorder ( SAD ) that was in clinical remission after light therapy .  METHODS Patients who met DSM-III-R criteria for recurrent major depressive episodes , seasonal ( winter ) pattern ( equivalent to SAD ) , were treated with a st and ard course of light therapy .  Ten patients with SAD in clinical remission after light therapy  underwent rapid tryptophan depletion in a placebo-controlled , double-blind crossover study . Behavioral ratings and plasma tryptophan levels were obtained before and after rapid tryptophan depletion . RESULTS Plasma total and free tryptophan levels were significantly reduced to 20 % of normal levels by the rapid tryptophan depletion . The depletion session result ed in significant increases in depression scores compared with the sham control session . Six of 10 patients had a clinical ly significant relapse of their depression following the tryptophan depletion session . CONCLUSIONS Rapid tryptophan depletion appears to reverse the antidepressant effect of bright light therapy in patients with SAD . This suggests that the therapeutic effects of bright light in SAD may involve a serotonergic mechanism
Recent systematic review s have shown that  light therapy  is an efficacious and well-tolerated treatment for SAD .
There is also evidence for efficacy of pharmacotherapy to treat and prevent SAD .
SAD is a common condition with significant psychosocial impairment .
BACKGROUND Seasonal affective disorder ( SAD ) consists of recurrent major depressive episodes in the fall/winter with remissions in spring/summer .
RESULTS A careful history is important to make the diagnosis and differentiate SAD from other similar conditions such as subsyndromal SAD and atypical depression .
Seasonal patterns with winter worsening are also recognized in " nonseasonal " depression as well as many other psychiatric conditions , and comorbidity with SAD is common .
The pathophysiology of SAD seems to be heterogeneous as research on circadian , neurotransmitter function and genetic hypotheses have shown discrepant results .
A dual vulnerability model with differential loading on separate seasonal and depression factors has been proposed to explain these findings .