Which supplement is commonly used to regulate sleep-wake cycles and circadian rhythm?

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

Answer: (C)

Melatonin is the supplement that regulates sleep-wake cycles and circadian rhythm. It’s a hormone produced by the pineal gland in response to darkness, signaling the body that it’s time to sleep and helping align our internal clock with the day-night cycle. Taking melatonin can help adjust sleep timing in situations like jet lag, shift work, or insomnia tied to circadian misalignment. The other substances don’t serve this clock-regulating role: garlic is used for other health effects, St. John’s Wort mainly affects mood through monoaminergic pathways and doesn’t entrain circadian rhythms, and black cohosh is used for menopausal symptoms.