An opioid is a type of drug that is used to relieve pain and produce feelings of euphoria and relaxation. Opioids may be natural (e.g. opium) or synthetic (e.g. fentanyl). They work by binding to opioid receptors in the brain, spinal cord, and other parts of the body, which are part of the body’s natural pain-relief system. Opioid drugs can help manage severe pain, such as cancer or after surgery, or to treat conditions like coughing, diarrhoea, and opioid-induced constipation. They are highly addictive and have a number of side effects.