from the mayo clinic:
“melatonin side effects may include:
Daytime sleepiness, Dizziness, Headaches, Abdominal discomfort, Confusion, Sleepwalking, Nightmares.
Melatonin may interact with various medications, including:
Blood-thinning medications (anticoagulants), Immunosuppressants, Diabetes medications, Birth control pills.
It’s thought that taking melatonin for longer than two months may be harmful, and the best dose of melatonin isn’t certain.
If you take melatonin, make sure the supplements are made of artificial ingredients, not made from animals. Melatonin from animals can contain viruses or other contaminants.”