Before you take melatonin, check with your doctor if you have any existing health conditions. According to drugs.com, which is powered in part by the American Society of Health-System Pharmacists, Harvard Health and Mayo Clinic, you should take caution -- and ask your doctor if you can take melatonin -- if you have any of the following health conditions:  High blood pressure (hypertension) Low blood pressure (hypotension) Diabetes Depression A bleeding or blood clotting disorder Epilepsy or seizures An autoimmune condition You should also check with your doctor about melatonin drug interactions if you're currently on any other medications, including other sedatives.  Remember, when taking any dietary supplement, use it wisely.