Melatonin supplementation might impact dreams, but it’s hard to say much with certainty. Theoretically, melatonin could promote dreaming by increasing time spent in REM, a primary sleep stage when dreaming occurs. One randomized controlled trial of 22 young adults did find that taking melatonin before bed increased how bizarre participants rated their dreams.[1] However, aside from this small study, there isn’t much research confirming a dream-enhancing or dream-altering effect of melatonin. In two randomized controlled trials of people with sleep disorders, melatonin supplementation increased time spent in REM but had no obvious effect on the number, intensity, or quality of dreams.[2] And another study of 30 people with Parkinson’s disease found melatonin supplementation had no apparent effect on the frequency of vivid dreams compared to placebo.[3]
In some studies, people have stopped taking melatonin due to nightmares, although this is a rare occurrence.[4][5] It’s also not clear whether the nightmares were caused by melatonin or just happened to occur while the person was taking melatonin. Furthermore, one randomized controlled trial reported no increase in the rates of nightmares with melatonin supplementation.[6]