What is a GLP-1? Single, dual and triple agonists explained

Updated 2026-10-15 · The Pep Planner

GLP-1 is probably the most searched term in this space right now, and the names pile up fast. Here is what GLP-1 actually is, what "agonist" means, and how the compounds you hear about differ from each other.

GLP-1 is a natural gut hormone

GLP-1 stands for glucagon-like peptide-1. It is a peptide hormone your gut releases after you eat, and it acts on GLP-1 receptors in several parts of the body.

Natural GLP-1 breaks down within a few minutes of being released, so it only acts briefly.

What a receptor agonist is

An agonist is a molecule that switches on a receptor, the way the natural hormone does. GLP-1 receptor agonists are peptides modified to act on that receptor but last far longer in the body, often by adding a fatty acid chain or changing a few amino acids.

Single, dual and triple agonists

Newer compounds act on more than one hormone receptor. The tags below show which receptors each one targets.

Semaglutide: GLP-1 (single)
Tirzepatide: GIP and GLP-1 (dual)
Mazdutide: GLP-1 and glucagon (dual)
Retatrutide: GIP, GLP-1 and glucagon (triple)
Cagrilintide: amylin, not GLP-1, but often discussed alongside them

Approved medicines vs. research vials

Some of these compounds are active ingredients in approved prescription medicines; others are still investigational. Vials sold "for research use only" are not approved for human use, whatever compound is on the label, and the FDA has warned about unapproved and counterfeit GLP-1 products.

Keeping the names straight

Compound name: the ingredient, like semaglutide
Brand name: the product an approved medicine is sold under
Shorthand: "sema," "tirz," "reta" and similar nicknames used in forums
Use the full compound name in your records so your history stays searchable

How The Pep Planner fits in

Protocols with these compounds often move through phases. In The Pep Planner each step is saved on the protocol, the calculator works out the strength of each mixed vial, and your stock counts down as you check off days. Each compound has its own neutral profile in Resources if you want the background.

Common questions

Is a GLP-1 a peptide?

Yes. Natural GLP-1 is a peptide hormone, and the GLP-1 receptor agonists mentioned here are modified peptides.

What does GIP stand for?

Glucose-dependent insulinotropic polypeptide, another natural gut hormone that dual and triple agonists also act on.

Try The Pep Planner free: 14-day trial, no card needed.