what is the side effect of melatonin?
 Change in sleep pattern; headache. Severe allergic reactions (rash; hives; difficulty breathing; tightness in the chest; swelling of the mouth, face, lips, or tongue); confusion; depression; fast heartbeat; hypothermia (fast breathing, shivering). 
Less common melatonin side effects might include abdominal discomfort, mild anxiety, irritability, confusion and short-lasting feelings of depression. 