OPIATE AGONISTS AND ANTAGONISTS

Agonist:
A drug or medication that can interact with brain nerve receptors to stimulate drug actions or effects.

Full opioid agonist:
A drug or medication that stimulates activity at opioid receptors in the brain that are normally stimulated by naturally occurring opioids. Examples of full opioid agonists include morphine, methadone, oxycodone, hydrocodone, heroin, codeine, meperidine, propoxyphene, and fentanyl.

Partial opioid agonist:

A drug or medication that can both activate and block opioid receptors, depending on the clinical situation. Under appropriate conditions, partial agonists can produce effects similar to those of either agonists or antagonists. Buprenorphine is a partial opioid agonist.

Antagonist:

A drug or medication that prevents molecules of other drugs/medications from binding to a receptor (eg, an opioid receptor). Antagonists can also displace other opioids and can precipitate withdrawal, or block the effects of other opioids. Examples of antagonists include naltrexone and naloxone.