According to MayoClinic.com, the most common melatonin side effects include nausea, vomiting, irritability, cramping, drowsiness, headache, lightheadedness and tiredness. These effects can possibly occur if you take melatonin in the morning or consume high doses. Some individuals have also reported to suffer more vivid dreams and nightmares, sleepwalking and confusion while they use melatonin. What could also accompany melatonin usage is a slight risk of infection or possibly an allergic skin reaction.
According to MayoClinic.com, melatonin can result to problems with blood clotting and must be avoided by people who are already using blood thinners or those who have clotting disorders. This supplement can also lead to reduced blood pressure which can be harmful if the person has already low blood pressure or is taking drugs which can lower the blood pressure.