GLP-1, GIP and glucagon agonists: what “dual” and “triple” mean

Single agonists: one receptor, one signal

Semaglutide and liraglutide are GLP-1 receptor agonists: they bind and activate one receptor, the glucagon-like peptide-1 receptor. GLP-1 is a hormone the gut releases after eating, and drugs built around it were the first in this family to reach wide clinical use and, later, a research-chemical market selling the same molecules outside the prescription channel.

Dual agonists: tirzepatide adds a second receptor

Tirzepatide activates two receptors instead of one: GLP-1 and GIP, the glucose-dependent insulinotropic polypeptide receptor. Eli Lilly's SURPASS clinical trial program tested it head-to-head against selective GLP-1 agonists including semaglutide, and it's now the reference compound researchers use when studying what adding GIP activity on top of GLP-1 changes. That reference role is explicit in Core Power Peptides' own tirzepatide listing, which describes the compound as “a benchmark for GIP/GLP-1 synergy research and a benchmark for emerging triple agonist compounds including retatrutide.”

As a pharmaceutical, tirzepatide is FDA-approved and sold by prescription under other brand names. What research-peptide vendors sell is a separately sourced, non-prescription version of the same sequence, marketed for laboratory use rather than through that approval. Our guide on what research-use-only labeling does and doesn't mean covers what that distinction does and doesn't settle.

Triple agonists: retatrutide adds a third

Retatrutide goes a step further, activating three receptors: GLP-1, GIP and the glucagon receptor. Eli Lilly has been developing it under the TRIUMPH Phase 3 trial program. The last time we checked, retatrutide remained investigational and had not received FDA approval as a drug. That doesn't mean no one sells it as a research peptide: Peptryn stocks it directly, in 10mg, 30mg and 60mg sizes, with two published lot-matched certificates. Core Power Peptides and Peptides for Sale do not carry it.

That third receptor, glucagon, is the mechanistic reason retatrutide gets described as the next step past dual agonists. It's also exactly why a vendor's tirzepatide is not a substitute for retatrutide in any research sense; they activate a different number of pathways, and a study designed around one doesn't transfer to the other.

If you specifically want retatrutide, not tirzepatide

We get asked about retatrutide because it's the most-discussed compound in this class right now, and this guide previously said no vendor we'd reviewed stocked it. That was wrong: Peptryn sells retatrutide directly, and it's also the top-documented vendor of the four we check, with two batch-matched certificates for it. American Peptides, which we added on 8 October 2026, lists it too, in five sizes with a certificate for each. If retatrutide itself, not the dual-agonist tirzepatide, is what your research calls for, Peptryn is where we'd point you first.

Our featured partner, Core Power Peptides, doesn't carry retatrutide. We still point most readers to tirzepatide from Core Power Peptides by default, because we've chosen to partner with that vendor for reasons laid out on our comparison page — but that's a commercial choice on our part, not a claim that tirzepatide is a substitute for retatrutide, or that retatrutide isn't available. It is, and Peptryn's paperwork for it is the strongest we've seen from any of the four vendors, for any product.