According to study data published in the Journal of Psychiatric Research, melatonin administered following acute coronary syndrome (ACS) had no prophylactic effect on the development of depression. The efficacy of melatonin, which has shown a prophylactic antidepressant effect in breast cancer, was explored given the prevalence of depressive symptoms after ACS.

Lead investigator Michael Tvilling Madsen, PhD, of the department of surgery, Zealand University Hospital, Lykkebaekvej in Køge, Denmark, and colleagues conducted the study as part of a double-blinded placebo-controlled randomized clinical trial carried out at 5 primary care cardiology departments in Denmark.

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Adult patients without depression at baseline were enrolled within 4 weeks of hospital admission for ACS. Patients were randomly assigned to receive either 25 mg of melatonin or placebo 1 hour before bedtime for 12 weeks. The primary outcome measure was incidence of depression defined as Major Depression Inventory (MDI) score ≥21 assessed every 2 weeks in the trial. Safety outcomes, including harm and adverse events, and the Hospital Anxiety and Depression Scale (HADS) were also assessed.

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Two hundred fifty two screened patients were randomly assigned to receive treatment, equally split between melatonin and placebo. Baseline MDI scores were 6.18 and 5.98 in the melatonin and placebo groups, respectively.

No significant between-group differences in MDI score were observed in the intention-to-treat or per-protocol analyses.

At 12 weeks, cumulative incidence of depression was 6 cases in the melatonin group and 4 cases in the placebo group. A significant overall decline in MDI scores was observed during the study period (P =.0002). There were no differences in HADS scores between the groups or in terms of adverse events.

These data show no prophylactic effect of 25 mg melatonin vs placebo on depression following ACS.

Study limitations include the low incidence of depression and low participation rate among screened participants, which may have an impact on external validity.

“The non-significant results might be due to a type II error,” denoting an erroneous failure to reject the null hypothesis, “or melatonin might not be able to prevent development of depressive symptoms following ACS,” the study investigators wrote.


Madsen MT, Zahid JA, Hansen CH, et al. The effect of melatonin on depressive symptoms and anxiety in patients after acute coronary syndrome: the MEDACIS randomized clinical trial [published online September 30, 2019]. J Psychiatr Res. doi:10.1016/j.jpsychires.2019.09.014