Treatments for depression are difficult to study. First, depression is a condition that can improve without treatment. So any treatment must be compared to placebo to see if the treatment is responsible for the improvement or if the depression improved on its own. Also, depression can not be measured objectively. There is no objective test like an X ray or a blood test that can diagnose depression. (At least not yet. As our understanding of brain function improves, such a test is certainly conceivable.) For now, the most reliable measures of depression used in research are standardized questionnaires. Another difficulty is that depression has a high response rate to placebo, so demonstrating that a treatment is better than placebo isn’t easy.
Because of these difficulties, most randomized trials testing antidepressants tend to study severely depressed patients, and they clearly show that antidepressants are beneficial. But is the benefit the same in patients with milder depression? A study in this issue of the Journal of the American Medical Association answers that question.
The study collected the data from six trials which randomized a total of 718 patients with depression to an antidepressant or to placebo. It then compared how much more improvement antidepressants offered over placebo in patients with different levels of depression severity. Surprisingly, for patients with mild or moderate initial symptoms, the difference between antidepressant and placebo was not significant. The benefit of antidepressants over placebo grew in those with more severe symptoms.
The authors conclude:
The magnitude of benefit of antidepressant medication compared with placebo increases with severity of depression symptoms and may be minimal or nonexistent, on average, in patients with mild or moderate symptoms. For patients with very severe depression, the benefit of medications over placebo is substantial.
What does that mean in practical terms? First, it’s another reminder that antidepressants help patients with severe depression. But for patients with mild symptoms it suggests that the visit with an attentive doctor, the anticipation that the medication may work, and the simple passage of time help more than the medicine itself.
Wall Street Journal article: Effectiveness of Antidepressants Varies Widely
Journal of the American Medical Association article: Antidepressant Drug Effects and Depression Severity