Also known as: There are no other common names for melatonin.

Potential uses: In its natural form, melatonin is a hormone that plays a role in regulating the body’s sleep cycle. Some people use melatonin supplements to ease sleep problems or jet lag. Melatonin may help to alleviate depression, anxiety, and fatigue. It’s also claimed that melatonin is an antioxidant that reduces cell damage and boosts the immune system.

Usual dose: There are no set recommendations for dosing or how long to use melatonin. A range of anywhere from 0.5 milligrams to 5 milligrams per day has been suggested.

Are there any risks? Although short-term use of melatonin appears safe, melatonin’s potential risks are not fully understood. According to the American Cancer Society, some users have reported headaches, drowsiness, and confusion, as well as nightmares and trouble sleeping when taking melatonin at high doses. Melatonin may interact with blood thinners and medications used to treat diabetes and seizures. It also may affect reproductive hormone levels in women. It generally is not recommended for those with severe mental illness, high blood pressure, or heart disease.

What does the research show? Some studies have found that women with lower levels of melatonin, such as those who work the night shift or sleep fewer hours, have a higher risk of developing breast cancer. In the lab, melatonin appears to slow the growth of breast cancer cells. Whether melatonin supplements can help prevent or even treat breast cancer is yet to be determined. Much more research is needed. Researchers also are looking at whether melatonin can improve quality of life in people who’ve been diagnosed with cancer, either alone or in combination with other treatments.