There have been a good number of previous studies on light therapy for bipolar disorder. Some studies with this treatment modality, compared to probably inactive controls, have not shown efficacy for patients whose disease does not have a seasonal component. Other reports have suggested a high rate of transition to mania in patients with bipolar disorder when given early morning light (the usual time for light therapy targeting non-bipolar depression). Fortunately, 2 studies have shown good results for chronotherapy; in these studies, patients were kept awake overnight and then administered morning light.2 However, midday light might be safer and / or more effective based on some theoretical considerations, and more acceptable in relation to sleep deprivation.
In a small midday light study, 46 patients with moderate bipolar depression were randomized to receive 1 hour of bright white light at noon (7,000 lux, which is less than the 10,000 lux usually given for unipolar depression) or 50 lux of weak red placebo light for 6 weeks.1 Patients with mixed characteristics, as well as those with a history of rapid cycles within the past year, were excluded from the study. Patients with active suicidal ideation, those with substance use disorder within the past 6 months and those on melatonin, stimulants or nonsteroidal anti-inflammatory drugs were also excluded. Thus, at best, the results of the study apply to a very limited number of patients compared to patients in usual practice.
The light dose was titrated slowly as a precaution against the induction of mania. Participants started with a 15-minute treatment, which increased by 15 minutes per week to reach 1 hour by week 4. Most other light treatment regimens start with the full dose, so this was usually done. ‘another new aspect of the approach (in addition to the light schedule).
The results demonstrated that remission (defined as a score of 8 or less on the Primary Depression Rating Scale) was observed at week 6 in 68% of the bright light group versus 22% of the control group. There were no mood polarity switches. Notably, there was no difference between the active and placebo groups during the first 3 weeks. Remission in other light therapy studies tended to cluster at week 5, so the time to improvement was similar to other protocols despite increasing the dose in the first 4 weeks. However, based on the difference in improvement observed between the active and placebo groups over weeks 4-6, it seemed likely that a longer treatment duration could have resulted in additional remissions for the treatment group. The conclusions were characterized as robust, which is a term rarely encountered in studies of bipolar depression (except, perhaps, for electroconvulsive therapy).3
Efforts have been made to avoid bias among patients regarding their expectations of bright light versus weak red light. The recorded baseline expectation levels were equal in the 2 groups and did not change when repeated at the end of the study. Nevertheless, one cannot be extremely sure that the blind man succeeded when the treatments seemed so different.
Nothing is known about the strategies to be used with morning light to maintain therapeutic effects.
The caution should be offered that new treatments often work well in early studies, but then these results are more difficult to replicate in later, larger studies. Examples of such include valproate and prazosin.4.5
Dr Osser is Associate Professor of Psychiatry at Harvard Medical School and Co-Chief Psychiatrist, US Department of Veterans Affairs, National Telemental Health Center, Bipolar Disorders Telehealth Program, Brockton, Massachusetts. He is also a member of the editorial board of Psychiatric schedulesMT. Dr. Osser has no financial disclosure regarding this article.
1. Sit DK, McGowan J, Wiltrout C, et al. Adjunct bright light therapy for bipolar depression: a randomized, double-blind, placebo-controlled trial. Am J Psychiatry. 2018; 175 (2): 131-139.
2. Benedetti F, Riccaboni R, Locatelli C, et al. Rapid response to treatment of suicidal symptoms with lithium, sleep deprivation, and light therapy (chronotherapy) in drug-resistant bipolar depression. J Clin Psychiatry. 2014; 75 (2): 133-140.
3. Wang D, Osser DN. The Psychopharmacology Algorithm Project at the Harvard South Shore Program: An Update on Bipolar Depression. Bipolar disorder. 2020; 22 (5): 472-489.
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5. Osser DN. Comorbid PTSD: update on the role of prazosin. Psychiatric schedules. 2021; 38 (4): 21. ❒