Bright light therapy works in bipolar disorder the same way it does in depression. However, bipolar is not the same as major depression. The depressive state may also switch to another, too enthusiastic, state of mood dangerous for its disinhibited behaviour. Are there any risks of phototherapy triggering mania?
Historically, there were two contradicting arguments:
- On one hand, we are talking about light, about a lamp mimicking the effects of a sunny day. Therefore, it sounds silly to think of any dangers, unless you would consider nice weather to be a threat?
- On the other hand, mania and hypomania are linked to the dopaminergic system of the brain and dopamine is affected by light as well as the placebo effect. Therefore, as long as the subject knows about being treated, there is always an increased risk of manic or hypomanic response. Moreover, through the sophisticated mechanisms of circadian regulation, the bright light therapy also targets dopamine, which might increase this risk.
Luckily, we have research studies directly examining the possibility of light therapy triggering mania or hypomania with reassuring results: there is no reason to expect the worst.
Research studies consistently report only a subtle increase in the risk of mania. While antidepressant drugs trigger mania in 15-40% of bipolar patients, the largest analysis of (hypo)manic switch in bright light therapy only found it to be around 2-3%. However, because there still is some risk, bright light therapy is usually used in addition to treatment with mood stabilizers that should prevent the mania switch, no matter whether it might be triggered by bright light or something else.
In the past, some scientists were warning against using bright light in bipolar disorder, but those warnings no longer apply. An overview from 2019 concludes that bright light therapy is safe to use with mood stabilizers and recommends planning the daily light exposure for noon rather than morning, which is the standard in depressions generally. Moreover, this advice is only based on very limited data and many clinicians and scientists do not see the need to consider noon as more optimal than morning.
The highest reported rate of a switch from bipolar depression into mania after LT is similar to the 4% switch rate expected during the placebo treatment of BD, thus not justifying specific concerns when using this treatment option.Benedetti, F. (2018). Rate of switch from bipolar depression into mania after morning light therapy: A historical review. Psychiatry Research 261, 351-356.
Bright light therapy was found safe in bipolar disorder when applied together with mood stabilizing medication. Nevertheless, bipolar disorder does require medical supervision to prevent manic or hypomanic switches. To be on the safe side, when starting with bright light therapy to treat bipolar, you may simply email the link to this website to your psychiatrist who can provide you with individual guidelines if necessary.
For practical information, see our guidelines for light therapy in depression.