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Seasonal affective disorder (SAD)

 

As we enter the shortest days of the year, some patients may experience depression and for many this is a recurring event. Recurrent major depressive disorder with seasonal pattern, more commonly known as seasonal affective disorder (SAD), affects two to three per cent of all Canadians.1 A milder form ("winter blues") affects up to 10 to 20 per cent.2 Symptoms generally occur in the fall or winter and remit by spring, though a minority of patients experience the opposite pattern (summer SAD). The incidence increases with latitude, and is more common between 20 and 50 years, and in women.1-3 The etiology of SAD remains unclear, but it is hypothesized that circadian rhythms and genetic factors are involved, and that serotonin, catecholamines, and melatonin also play a role.1

 

Light therapy remains one of the main treatments for winter SAD.4,5 However, questions remain about what is optimal light therapy (e.g. spectrum and intensity/dose).6,7 A Swedish health technology assessment found that light therapy improved depression scores in the first few weeks of therapy compared to placebo, but the effect diminished over time.5 Light therapy had no benefit when looking at clinical response (a 50 per cent reduction in depression score) as the outcome. Side effects, however, tend to be mild and include agitation, headache, eye strain and nausea. Hypomania has been reported with the initiation of light therapy. Blue wavelength light may harm the retina.

 

Various drug therapies have been studied for SAD (Table 1), with the majority of studies focusing on SSRIs and newer antidepressants. Although there are many reports of positive effects with medications, the quality of evidence overall is also poor. Of note, tricyclic antidepressants are not recommended since their sedating effects can exacerbate sleepiness and lethargy that accompanies SAD8, and there is a lack of evidence of benefit.

 

Extended-release bupropion is the only pharmacological therapy officially indicated for the prevention of SAD,9,10 although other serotonergic antidepressants may also be effective.11 Preventative treatment is usually started in the fall before the anticipated onset of symptoms, and tapered off in the spring, four to six months later.

 

Light therapy or drug therapy?

There are few direct comparisons between light therapy and medication so it is not possible to make a specific recommendation. Initial treatment decisions may be made on factors such as preference, convenience, and costs. Light therapy is considered generally "low risk",4 but does require a daily time commitment.12 A recent Canadian study comparing the total health care costs of light therapy versus fluoxetine (two therapies that have been reported to be equally effective) found that while purchasing a light box might cost more up front, after the first year of treatment light therapy starts to cost less, especially if fluoxetine doses are greater than 20 mg/d.13

 

Summary:

Patients suffering from seasonal affective disorder may benefit from light or drug, but the overall quality of evidence, especially for drug therapy is low. Bupropion is the most effective drug treatment.

 


References:

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  6. Swedish Council on Technology Assessment in Health Care. Light Therapy for Depression, and Other Treatment of Seasonal Affective Disorder. A Systematic Review. http://www.sbu.se/upload/Publikationer/Content1/1/light_therapy_depression.pdf. Accessed 08/11/2012.
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©2013 B.C. Drug and Poison Information Centre


A version of this document was published in BCPhA's The Tablet. 2012; 21(6): 24-5.

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