Opioids are potent drugs used to treat severe pain. Opioids are derived from the opium poppy plant and produce the effect of dulling the senses and sometimes inducing sleep.

Side effects of opioid use can include impairment of mental function, drowsiness, constipation, respiratory depression, and possibly addiction. For these reasons opioids are only rarely used to treat chronic pain.

Opioid and natural endorphin molecules compete to reach receptors on neurons. Once they attach to the receptors, pain signals are blocked.