The term “opioids” refers to both natural and synthetic derivatives of opium. This includes street drugs such as heroin; and prescription analgesics such as morphine, tramadol, oxycodone, or fentanyl. Opioids may be prescribed for pain relief, cough suppression, or to control diarrhea. They act as agonists for different opioid receptors, including the delta, kappa and mu opioid receptors. However, the potential for addiction is extremely high, as is the risk of overdose, particularly with stronger agents such as heroin and fentanyl.

Patients often report feelings of euphoria and relaxation. These relatively pleasant sensations are referred to as “the high” and the desire to return to this state is what often drives them to relapse. This is caused by dopamine receptor stimulation.

Patients may have a positive history of opioid use disorder. Alternately, they may have a history of drug-seeking behavior, or the patient's families and friends may advise the hospital staff that they are a known opioid user.