Why scientists combine GLP-1 with other hormones
GLP-1 alone helps, but it works through only one pathway. Scientists are now combining GLP-1 with other gut hormones so weight loss comes from several angles at once.
You have heard of GLP-1 medicines like semaglutide. They help people feel full and lose weight. But scientists are now making a new kind of medicine. Instead of using GLP-1 alone, they combine GLP-1 with other body hormones. These are called multi-agonist drugs (say: ag-uh-nist). 'Agonist' means a key that turns on a lock. Each hormone turns on a different lock in the body. This short article explains, in plain words, why scientists think combining hormones can beat GLP-1 alone.
What is a hormone, and what does 'agonist' mean?
A hormone is a tiny messenger chemical the body makes. It travels in the blood and tells organs what to do. GLP-1 is one such messenger, made in the gut after you eat. An 'agonist' is a medicine that copies a hormone and switches on its receptor (the lock). A multi-agonist drug is one single medicine that switches on two or three hormone locks at the same time. The big idea: each hormone works through a different pathway in the body. So combining them attacks weight from several sides at once, not just one. A 2023 review calls these 'so-called gut hormone co-agonists as a new class of drugs for the treatment of diabetes' and obesity.
The four hormones and what each one does
Why not just take more GLP-1 instead of mixing hormones?
mostly falsemostly false — explained simply. GLP-1 only turns on one receptor, so it works through one main pathway (fullness and glucose). Turning up the dose does not add a new pathway, and higher doses bring more nausea and stomach side effects. Combining GLP-1 with GIP, glucagon, or amylin switches on different receptors at the same time. Preclinical studies show a GIP/GLP-1 co-agonist gave 'greater decreases in body weight and food intake...when compared to equal doses of either exendin-4 or liraglutide' (both GLP-1-only). Each added hormone pulls weight through a separate channel: appetite, energy burn, and glucose control.
Tirzepatide is the proof that combining helps
Tirzepatide (Mounjaro, Zepbound) is the first dual GIP/GLP-1 medicine already approved for doctors to use. It is the real-world proof that adding a second hormone helps. In the SURMOUNT-1 trial in adults with obesity, the 15-mg weekly dose gave a mean weight loss of about -20.9% over 72 weeks. That is more than GLP-1-only semaglutide achieved in its own trial. The reviewers call tirzepatide 'the first monomeric peptide with dual activity at both incretin receptors now available for clinical use'. So the 'combine hormones' idea is not just theory, it already works in approved medicine.
Triple agonists and amylin combos are still being tested
Most triple and amylin-combination drugs are still investigational (say: in-ves-tig-AY-shun-al). That means they are still in clinical trials, not yet approved for you to take. Retatrutide is a triple GIP/GLP-1/glucagon agonist. In a phase-2 trial the 12-mg weekly dose 'yields a 24.2% reduction in total body weight at 48 weeks'. That is even bigger than tirzepatide, but it is still being tested for safety in bigger trials. For amylin, the combo of cagrilintide plus semaglutide (CagriSema) is also still in trials. The honest takeaway: the mechanism makes sense, and the early numbers are exciting, but the clinical payoff is still being proven.
What this means for you, simply
The bottom line
Multi-agonist obesity drugs combine GLP-1 with other hormones like GIP, glucagon, and amylin so the body fights weight through several different pathways at once, not just one. Tirzepatide, already approved, proves that adding GIP helps. Triple and amylin combos are still being tested in trials. Talk to your doctor about what is approved and right for you, and do not chase a medicine that is not yet ready.