Opioid withdrawal is a set of symptoms (a syndrome) arising from the sudden withdrawal or reduction of opioids where previous usage has been heavy and prolonged. Signs and symptoms of withdrawal can include drug craving, anxiety, nausea, vomiting, diarrhea, sweating, and an increased heart rate. Opioid use triggers a rapid adaptation in cellular signalling pathways that means, when rapidly withdrawn, there can be adverse physiological effects. All opioids, both recreational drugs and medications, when reduced or stopped, can lead to opioid withdrawal symptoms. When withdrawal symptoms are due to recreational opioid use – the term opioid use disorder is used; when due to prescribed medications the term prescription opioid use disorder is used. Opioid withdrawal can be helped by the use of opioid replacement therapy, and symptoms may be relieved by the use of medications including lofexidine and clonidine.