Like all medications, melatonin can have side effects for some people. Those who experience side effects often find that they settle down within a few doses. Side effects include:Daytime sleepiness or tirednessHeadacheNausea (feeling sick)DizzinessDry mouthIrritabilityDry, itchy skinStrange dreamsNight sweatsPains in your arms or legs.Melatonin can also cause some rare but serious side effects. You should speak to a doctor if you experience:Low mood or sadnessBlurry vision or watery eyesFeeling confused or dizzyFainting or collapsingBleeding that won’t stop, excessive bruising or blood in your urinePsoriasis.If you have a severe allergic reaction (anaphylaxis) including breathlessness, lip or tongue swelling, call 999 immediately. If you have heart palpitations or chest pain, call 999 immediately.