Glossary

Agonist:
A drug or medication that attaches to and activates specific receptors to stimulate drug actions or effects.

Full opioid agonist:
A drug or medication that stimulates activity at opioid receptors in the central nervous system 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 stimulates activity at opioid receptors that does not produce the same maximal effects as a full opioid agonist. Like full opioid agonists this activity occurs at receptors that are normally stimulated by naturally occurring opioids. Under appropriate conditions, partial agonists can produce effects similar to either agonists or antagonists. Buprenorphine is a partial opioid agonist.

Antagonist:
A drug or medication that attaches to but does not activate specific receptors to stimulate drug actions or effects and can block other like-drugs/medications from binding to a receptor (e.g. an opioid receptor). Antagonists can also displace other drugs or medications. When an antagonist displaces an opioid, precipitate withdrawal can occur. Examples of opioid antagonists include naltrexone and naloxone.

These definitions are from suboxone.com