The most common effects of opioid overdose are vomiting, drowsiness, pinpoint pupils, bradycardia, convulsions and coma. Respiratory depression is common and may lead to cyanosisS and respiratory arrest. Hypotension occurs occasionally, and in severe cases non-cardiogenic pulmonary oedema and cardiovascular collapse may occur. Cardiac arrhythmia may occur with some opioids. Some opioids have a histamine-releasing effect which may result in an urticarial rash, pruritus, flushing and hypotension. Activated charcoal should be given following overdose and naloxone administered to reverse respiratory depression and deep coma.