Opioids are a class of drugs naturally found in the opium poppy plant and that work in the brain to produce a variety of effects, including the relief of pain with many of these drugs. Opioids can be prescription medications often referred to as painkillers, or they can be so-called street drugs, such as heroin.

People use opioids in the first place for pain relief (analgesia).

These include muscle and bone pain, restlessness, diarrhea, insomnia, cold flashes, goosebumps, vomiting. Withdrawal symptoms can be pretty severe depending on the length and severity of the addiction.

Due to their pharmacological effects, opioids can cause breathing difficulties, and opioid overdose can lead to death. Worldwide, about 0.5 million deaths are attributable to drug use.

Taking opioids over a long period of time produces dependence, such that when people stop taking the drug, they have physical and psychological symptoms of withdrawal (such as muscle cramping, diarrhea, and anxiety).