GLP-1 medications copy a hormone your gut already makes. Here is what that hormone does, how the medications change appetite and digestion, and which products are FDA-approved versus compounded.
GLP-1 medications have changed how obesity and type 2 diabetes are treated, and most people have heard the brand names by now. Fewer people can explain what the medication is actually doing inside the body. This guide walks through the hormone these medications are built on, what changes when you take one, what the clinical trials measured, and how FDA-approved products differ from compounded versions. It is educational only and does not determine whether any medication is right for you.
GLP-1 stands for glucagon-like peptide-1. It is a hormone released by specialized cells in the lining of your intestine within minutes of eating. In a 2018 review in Cell Metabolism, endocrinologist Daniel Drucker summarized its main jobs: it prompts the pancreas to release insulin when blood sugar rises, it suppresses glucagon (a hormone that pushes blood sugar up), it slows how quickly the stomach empties, and it reduces food intake by acting on appetite circuits in the brain.
In other words, GLP-1 is part of the body's "I have eaten, you can stop now" signal. The natural hormone is broken down within minutes, which is why your appetite returns a few hours after a meal.
A GLP-1 receptor agonist is a lab-made molecule that fits into the same receptors as natural GLP-1 but resists being broken down. Semaglutide, for example, is built so that it binds to a blood protein called albumin and stays active for about a week, which is why it is given as a once-weekly injection.
Because the signal is continuous rather than brief, the effects of the hormone are sustained:
A 2024 modeling paper from the National Institute of Diabetes and Digestive and Kidney Diseases offers a useful way to think about this. Its author, Kevin Hall, estimated that semaglutide and tirzepatide weaken the body's appetite feedback loop (the biological push to eat more as weight falls) by roughly 40 to 70 percent, compared with calorie restriction alone, which does not weaken it at all. That is why weight tends to keep falling for longer on these medications before it levels off.
Tirzepatide is slightly different. Its prescribing information describes it as a molecule that "selectively binds to and activates both the GIP and GLP-1 receptors." GIP (glucose-dependent insulinotropic polypeptide) is a second gut hormone released after meals. The combined action appears to produce larger average weight reductions than GLP-1 activity alone, which is covered in detail in our semaglutide versus tirzepatide article.
Two large placebo-controlled trials are the reference points for the current medications.
In STEP 1, published in the New England Journal of Medicine in 2021, 1,961 adults with obesity (or overweight plus a weight-related condition) and no diabetes received weekly semaglutide 2.4 mg or placebo for 68 weeks, alongside lifestyle counseling. Mean body weight changed by -14.9 percent in the semaglutide group versus -2.4 percent with placebo.
In SURMOUNT-1, published in the same journal in 2022, 2,539 adults received tirzepatide 5, 10 or 15 mg weekly or placebo for 72 weeks. Mean weight change was -15.0 percent, -19.5 percent and -20.9 percent respectively, versus -3.1 percent with placebo. The most common adverse events in both trials were gastrointestinal and mostly mild to moderate, clustering during the dose escalation phase.
These are averages from supervised trials with lifestyle support. Individual responses vary widely in both directions, and the figures should not be read as a prediction for any one person.
This distinction matters, and marketing often blurs it.
FDA-approved products. Wegovy (semaglutide) and Zepbound (tirzepatide) are approved for chronic weight management in adults with obesity, or overweight with at least one weight-related condition, alongside a reduced-calorie diet and increased physical activity. Wegovy also carries approvals for reducing major cardiovascular events in adults with established cardiovascular disease, and for a form of fatty liver disease. Zepbound is also approved for moderate to severe obstructive sleep apnea in adults with obesity. Ozempic and Mounjaro contain the same active ingredients but are approved for type 2 diabetes. All of these labels carry a boxed warning about thyroid C-cell tumors seen in rodent studies.
Off-label use. When a licensed provider prescribes an approved medication for a purpose, population or dosing pattern not on its label, that is off-label use. It is legal and common in medicine, but it means the specific use was not reviewed by the FDA. So-called "microdosing," meaning staying at doses below the labeled maintenance range, is an example of off-label dosing for which there are no large published outcome trials.
Compounded medications. Compounded semaglutide and tirzepatide are prepared by pharmacies rather than the original manufacturer. The FDA is clear that compounded drugs are not FDA-approved and are not reviewed for safety, effectiveness or quality before being sold. The agency has also published concerns about dosing errors, products arriving warm, and unlawful ingredients in some compounded GLP-1 products. Any compounded GLP-1 product offered through NewDay Wellness is a compounded medication and is not FDA-approved.
The approved labels list several situations where the medication should not be used or needs extra caution, including a personal or family history of medullary thyroid carcinoma or Multiple Endocrine Neoplasia syndrome type 2, a history of pancreatitis, pregnancy, and planned surgery under anesthesia. Reviewing your full health history with a licensed provider is part of any responsible prescribing process.
Mainly by quieting appetite. The continuous GLP-1 signal makes people feel full sooner and think about food less, and slower stomach emptying adds to fullness. A 2024 NIH modeling paper estimated these medications weaken the body's appetite feedback loop by roughly 40 to 70%.
A GLP-1 receptor agonist such as semaglutide activates one receptor. Tirzepatide activates both the GLP-1 and GIP receptors; GIP is a second gut hormone released after meals.
Because insulin release is boosted only when glucose is elevated, the risk of low blood sugar from the medication alone is low in people without diabetes. The risk is higher when combined with insulin or sulfonylureas.
No. Compounded semaglutide and tirzepatide are prepared by pharmacies, not the original manufacturer, and the FDA does not review compounded drugs for safety, effectiveness or quality before they are sold.
Understanding how a medication works is a good first step, but it is not the same as knowing whether it fits your health picture. A licensed provider can review your history, discuss approved and compounded options honestly, and set expectations that are realistic for you. Reading this article does not establish eligibility for any treatment.
Written by the NewDay Wellness editorial team from the sources above and checked against them before publication, and medically reviewed by Dr. Sean Arora and Dr. Shannon Arora of Arora Health & Aesthetics; see our editorial standards. This article is educational and does not diagnose conditions, establish eligibility for any medication, or replace care from a licensed provider. Compounded medications are not FDA-approved.
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