Associations between treatment with melatonin and suicidal behavior: a nationwide cohort study.

STUDY OBJECTIVES: Melatonin is often prescribed to patients with sleep disorders who are known to have elevated suicide risks. Yet, melatonin's association to suicidal behavior remains to be examined. We investigated whether individuals prescribed melatonin had higher rates of suicide and suicide attempts when compared to individuals who were not prescribed this drug, including both those with and without known mental disorders. METHODS: A cohort design was applied to longitudinal, register data on all persons aged 10+ years in Denmark during 2007-2016. Based on data from the National Prescription Register, periods of being in treatment with melatonin were defined using information on number of tablets and daily defined dose. We calculated IRR for suicide and suicide attempts, as identified in register records, comparing those in treatment with melatonin to those not in treatment. RESULTS: Among 5,798,923 individuals, 10,577 (0.2%) were treated with melatonin (mean treatment length 50 days) during the study period. Of those, 22 died by suicide and 134 had at least one suicide attempt. People in treatment with melatonin had a 4-fold higher rate of suicide (IRR: 4.8; 95% CI, 3.0-7.5) and a 5-fold higher rate of suicide attempt (IRR: 5.9; 95% CI,4.4-8.0) than those not in treatment and when adjusting for sex and age-group. CONCLUSIONS: Treatment with melatonin was associated with suicide and suicide attempt. While there are several possible explanations, attention to suicide risk is particularly warranted for people with mental comorbidity who are in treatment with melatonin.