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.