GLP-1 medications copy a natural hormone your gut releases after you eat. That hormone tells your brain you are full, slows down how fast your stomach empties, and helps your body handle blood sugar. Semaglutide and tirzepatide are longer-lasting versions of that signal, usually taken as a weekly injection.
Here is what is happening in the body, in plain language and without the hype, so you know what you are considering before you talk to a physician.
What is GLP-1?
GLP-1 stands for glucagon-like peptide-1. It is a hormone made by cells in your intestine when food arrives. It is one of several signals your gut uses to tell the rest of your body that you have eaten.
GLP-1 acts by attaching to GLP-1 receptors. These receptors are found in several places, including the brain, the stomach and the pancreas. That is why one hormone can affect appetite, digestion and blood sugar at the same time.
How does a GLP-1 medicine affect appetite?
In the brain, GLP-1 receptors sit in areas that help control hunger and fullness. When a GLP-1 medicine reaches those receptors, it sends a stronger, longer fullness signal than a meal alone.
This is a change in signals, not willpower. The medicine does not burn fat directly. It changes how hungry and how full you feel, and your eating habits, activity and sleep still matter. Physicians often pair a GLP-1 with simple habits, like eating slowly, choosing protein and fiber, and drinking enough water, which also help with stomach comfort.
Why does it slow stomach emptying?
GLP-1 also slows how quickly food leaves your stomach. Food stays in the stomach longer, which adds to the feeling of fullness after eating.
This same effect explains many common side effects. The FDA labeling for brand-name semaglutide and tirzepatide lists nausea, diarrhea, vomiting, constipation, stomach pain, decreased appetite and injection-site reactions as common side effects. Eating smaller meals and stopping when you feel full can help. If side effects are hard to manage, tell your physician. Our guide on what to do about GLP-1 side effects has more.
What does GLP-1 do for blood sugar?
In the pancreas, GLP-1 helps release insulin when blood sugar is high and lowers glucagon, a hormone that raises blood sugar. Because this response depends on blood sugar being high, GLP-1 on its own is less likely to push blood sugar too low. The risk of low blood sugar goes up when it is combined with insulin or sulfonylureas, which is one reason your physician asks about every medication you take.
GLP-1 medicines were first developed for type 2 diabetes, but you do not need diabetes to be considered for one for weight management. See do I need diabetes for a GLP-1?
How are semaglutide and tirzepatide different?
- Semaglutide acts on the GLP-1 receptor.
- Tirzepatide acts on the GLP-1 receptor and also on the GIP receptor. GIP (glucose-dependent insulinotropic polypeptide) is another gut hormone involved in blood sugar and energy balance.
Your body breaks down its own GLP-1 within minutes. Both medicines are built to last much longer, which is why they are usually injected under the skin once a week. Physicians typically start with a low dose and increase it gradually, which gives your stomach time to adjust. Your physician picks the medication and dose; you can share a preference.
Is compounded GLP-1 the same as the brand-name drugs?
No. Ozempic and Wegovy (semaglutide) and Mounjaro and Zepbound (tirzepatide) are FDA-approved brand-name drugs. Compounded semaglutide and tirzepatide are prepared by a licensed pharmacy for an individual patient with a valid prescription. They are not generic versions of the brands, and the FDA does not approve compounded drugs or review them before they are sold. Read our compounded medications disclosure and compounded vs brand-name GLP-1 for details.
Who should not take a GLP-1?
GLP-1 medicines are not a fit for everyone. The brand-name labeling carries a boxed warning about thyroid C-cell tumors seen in rodents, and people with a personal or family history of medullary thyroid carcinoma or MEN 2 should not take them. They are also not for people who are pregnant, breastfeeding or trying to conceive. Serious risks listed in the labeling include pancreatitis, gallbladder problems, kidney problems from dehydration and serious allergic reactions. A licensed physician reviews your history to screen for these.
Next step
If you want to know whether a GLP-1 could fit you, take the free assessment. A licensed physician in your state reviews it and decides. A prescription is never guaranteed.
VevaMD is a technology platform, not a medical provider. Educational content only, not medical advice. All prescriptions are written by independent board-certified physicians. Individual results vary.