GLP-1 Agonist
Also known as: GLP-1 receptor agonist · GLP-1RA · incretin mimetic
A GLP-1 agonist is a drug that activates the receptor for glucagon-like peptide-1 (GLP-1), a gut hormone, and is used to lower blood glucose and body weight.
GLP-1 is a hormone released from the gut after eating. GLP-1 receptor agonists mimic it but are engineered to last much longer than the natural hormone. Semaglutide, for example, has 94% sequence homology to human GLP-1, is modified at position 8 for stability against the enzyme DPP-4, and carries a fatty di-acid side chain that binds albumin. Its elimination half-life is about 1 week, which allows once-weekly dosing.
The class includes single GLP-1 receptor agonists such as semaglutide, as well as tirzepatide, which activates both the GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 receptors. According to the Wegovy label, GLP-1 is a physiological regulator of appetite and calorie intake, the GLP-1 receptor is present in brain areas involved in appetite, and semaglutide lowers body weight through decreased calorie intake. Because these drugs are long-acting, their effects and side effects build up over weeks, which is why the labels pair them with slow dose escalation.
Why it matters
This is the peptide class with the strongest human evidence. In a 68-week randomized trial of 1,961 adults with overweight or obesity, semaglutide 2.4 mg once weekly produced a mean body-weight change of −14.9%, compared with −2.4% on placebo. In a 72-week trial, tirzepatide produced −15.0%, −19.5%, and −20.9% at 5, 10, and 15 mg once weekly, compared with −3.1% on placebo.
That evidence comes with clear tradeoffs. Gastrointestinal effects such as nausea and diarrhea were the most common adverse events, and in the semaglutide trial 4.5% of participants stopped treatment because of them, versus 0.8% on placebo. The labels carry a boxed warning about the risk of thyroid C-cell tumors. The evidence also belongs to the approved products used on their label schedules; it does not transfer automatically to compounded or "research" versions whose identity and purity are unverified.
How to read a GLP-1 trial result
- Check what the drug was compared with: placebo, another drug, or nothing.
- Note the trial length and whether results were measured at the maintenance dose after titration.
- Read the mean change in both groups and look at the difference between them, not just the drug group's number.
- Look at how many people stopped because of side effects, not only at efficacy.
In the semaglutide trial, simple subtraction gives −14.9% − (−2.4%) = −12.5 percentage points. The trial reported an estimated treatment difference of −12.4 points, because that figure comes from a statistical model rather than raw subtraction.
Common mistakes
- Quoting the drug group's weight loss without accounting for the placebo group's change.
- Assuming trial results apply to compounded or research-grade products of unverified identity.
- Skipping the titration schedule, which the labels use to reduce gastrointestinal side effects.
- Treating GLP-1 drugs as interchangeable; tirzepatide also acts on the GIP receptor, and milligram doses do not translate between drugs.
Sources
- Clinical trialOnce-Weekly Semaglutide in Adults with Overweight or Obesity. N Engl J Med, 2021. PMID 33567185.
- Clinical trialTirzepatide Once Weekly for the Treatment of Obesity. N Engl J Med, 2022. PMID 35658024.
- Prescribing informationWEGOVY (semaglutide) injection, for subcutaneous use: Prescribing Information. U.S. Food and Drug Administration, 2021.
Page updated . How we grade evidence: methodology.
Related Terms
GLP-1 Receptor
The GLP-1 receptor is the G protein-coupled receptor that GLP-1 activates to boost insulin, lower glucagon, slow the stomach and reduce appetite.
GIP Receptor
The GIP receptor is the receptor for GIP, a gut incretin hormone that boosts insulin after meals; tirzepatide activates it along with the GLP-1 receptor.
Receptor Agonist
A receptor agonist is a molecule that binds a receptor and switches it on, producing a response the way the body's own signaling molecule does.
Peptide
A peptide is a short chain of amino acids joined by peptide bonds. US regulators treat chains of 40 or fewer amino acids as peptides.
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