Madsen MT, et al. - Researchers sought to ascertain if the development of depression could be prevented via administering melatonin following acute coronary syndrome (ACS). In this double-blinded, placebo-controlled, multicenter, randomized clinical trial, performed in five primary care cardiology departments at Zealand, Denmark, adult patients who were free of depression at baseline were included at the latest 4 weeks after acute coronary syndrome and were administered 25 mg melatonin or placebo 1 h before participants’ bedtime for 12 weeks. Randomization of 252 participants in a 1:1 ratio was done. Outcomes revealed no prophylactic antidepressant effect of melatonin following ACS. A type II error or inefficacy of melatonin in preventing the development of depressive symptoms following ACS may have led to the non-significant results.