Which supplement is commonly used to support mood and sleep through circadian rhythm effects?

• A. Garlic
• B. St. John's Wort
• C. Melatonin
• D. Black cohosh

Answer: (C)

Melatonin acts as a chronobiotic, signaling darkness to the brain and helping synchronize the body's internal clock with the external light-dark cycle. By nudging the timing of sleep-wake signals, it promotes sleep onset and regularity, which often leads to improved mood when circadian rhythms are disrupted. This makes it commonly used for jet lag, shift-work sleep problems, and delayed sleep phase syndrome—situations where aligning the circadian clock can also support mood. The other supplements don’t target circadian timing in the same way: garlic is more about general health effects, St. John’s Wort is an antidepressant that works through neurotransmitters and has many drug interactions, and black cohosh is used mainly for menopausal symptoms. So melatonin best fits the idea of supporting mood and sleep via circadian rhythm effects. Use should be guided by a clinician and timing/dosing kept appropriate to minimize daytime drowsiness.