Opioids are narcotics that act on opioid receptors to produce morphine-like effects. Medically they are primarily used for pain relief, including anesthesia. Other medical uses include suppression of diarrhea, replacement therapy for opioid use disorder, reversing opioid overdose, suppressing cough, and suppressing opioid induced constipation. Extremely potent opioids such as carfentanil are only approved for veterinary use. Opioids are also frequently used non-medically for their euphoric effects or to prevent withdrawal.