GLP-1 Agonists vs. Antagonists vs. Inhibitors

Short answer: the medications used for diabetes and weight loss, semaglutide and tirzepatide included, are "GLP-1 receptor agonists." An agonist activates a receptor; an antagonist blocks it. The two aren't interchangeable, and "GLP-1 antagonist" and "GLP-1 inhibitor" are not weight-loss drug categories.

Agonist: activates the receptor

An agonist is a substance that binds to a receptor and triggers the same response the body's natural signal would. GLP-1 receptor agonist medications bind to GLP-1 receptors and mimic the effects of the naturally occurring hormone, this is the mechanism behind semaglutide, tirzepatide, and similar medications.

Antagonist: blocks the receptor

An antagonist binds to a receptor but blocks it rather than activating it, preventing the natural hormone from having an effect. GLP-1 receptor antagonists exist as research tools used to study GLP-1 biology, they are not weight-loss or diabetes medications, and searching for a "GLP-1 antagonist" weight-loss product will not turn up a legitimate one.

Where "inhibitor" fits in

"GLP-1 inhibitor" is sometimes used loosely online, but it isn't a standard pharmacology term for this drug class. You may be thinking of DPP-4 inhibitors, a related but separate class of diabetes medications that work by blocking the enzyme that breaks down your body's own GLP-1, extending its natural effect rather than mimicking it directly.