Side effects are uncommon in patients treated with Circadin, but the most common side effects (seen in between 1 and 10 patients in 1,000) are irritability, nervousness, restlessness, insomnia, abnormal dreams, migraine, psychomotor hyperactivity (restlessness with increased activity), dizziness, somnolence (drowsiness), abdominal (tummy) pain, constipation, dry mouth, hyperbilirubinaemia (raised blood levels of bilirubin, a breakdown product of red blood cells, which can cause yellowing of the skin and eyes), hyperhidrosis (excessive sweating), asthenia (weakness) and increased weight.