A neat understandable summary…

Opioid: A drug that reduces pain signals to the brain and calms the emotional reaction to pain by binding to opioid receptors. The term “opioid” encompasses drugs derived from the opium plant – known as opiates—as well as synthetic drugs that work in the same way. Opiates include codeine and morphine. Synthetic opioids include oxycodone and hydrocodone.

Narcotic: An imprecise term for drugs that affect the brain and are subject to abuse. “Narcotic” is often used to refer to illegal drugs such as cocaine, heroin and marijuana (but of those, only heroin is an opioid).

Tolerance: A state in which the body no longer responds to a drug as in the past and requires higher doses to achieve the same effect.

Opioid-induced hyperalgesia: A condition in which long-term use of opioid drugs causes new or worsening pain.

Dependence: The condition in which the body functions normally only in the presence of a drug and withdrawal occurs when the drug is stopped. One can be dependent on a drug without being addicted.

Addiction: A compulsive use of drugs for non-medical reasons and despite negative consequences, characterized by an inability to stop using the drug and failure to meet family, work or social obligations.