Rate of switch from bipolar depression into mania after morning light therapy: A historical review

Light therapy (LT) is efficacious for bipolar depression with effect sizes equivalent to those in antidepressant pharmacotherapy trials. Patients with bipolar disorder (BD) show a 15-40% rate of manic switches during antidepressant drug treatment. The rate of manic switches during LT has never been estimated. We searched all the literature studies reporting effects of antidepressant LT in BD. 41 studies described 799 patients with BD treated with antidepressant LT, from among which 7 (0.9%) switched into mania and 11 (1.4%) switched into hypomania. The method of assessment of treatment-emergent symptoms significantly influenced the detection of switches into mania: 0% when no method was reported, 0.8% with clinical mental state examination, and 3% with rating scales (χ² = 14.805, d.f. 4, p = 0.005). The rate of switch increased to 18.8% when considering the 16 patients with rapid-cycling BD. Switches occurred independent of treatment modality (light intensity, duration, and circadian timing of administration). The available literature shows that the highest reported rate of switch from bipolar depression into mania after LT is closely similar to the 4% switch rate expected during the placebo treatment of BD, thus not justifying specific concerns when using this treatment option.