Scientific Glossary

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An agonist mimics or amplifies the effect of the body's natural signaling molecules. Full agonists produce the maximum possible receptor activation. Partial agonists activate the receptor but produce a submaximal response even at saturation. The distinction matters in research because partial agonists can act as functional antagonists by occupying receptors without fully activating them. GLP-1 receptor agonists like semaglutide are full agonists at the GLP-1 receptor.

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Antagonists occupy receptor binding sites competitively (reversible) or non-competitively (irreversible), blocking the receptor's activation. Unlike agonists, they do not trigger a response — they prevent one. Competitive antagonists can be overcome by increasing agonist concentration; non-competitive antagonists cannot. In peptide research, understanding the antagonist/agonist distinction is critical for interpreting mechanism studies that use receptor blockers to confirm which pathway a peptide acts through.