Opioids
Opioid drugs include morphine, codeine, oxycodone, hydromorphone, and methadone. These drugs are generally used for severe forms of acute pain. They may also be used for chronic pain conditions after other appropriate therapies have failed. Opioids act through several groups of receptors in the body, which is why they can have such a large and varied effect. There are guidelines for opioid therapy that should be followed to reduce risk of tolerance or addiction.