What is a GLP-1? How this class of medication works

What GLP-1 is, what the hormone does, and how GLP-1 medications work: how they are taken, what they are used for, side effects, and who can take one.

GLP-1 stands for glucagon-like peptide-1. It is a hormone your intestine releases when you eat: not a drug, but something your body already makes. In everyday use, 'a GLP-1' has also come to mean the medications built on it. This guide covers both: what the hormone does, what a GLP-1 medication is and how it works, and what to know before considering one.

What does the GLP-1 hormone do?

GLP-1 is made by L cells in the lining of the intestine and released into the bloodstream after a meal. It acts on several organs at once:

• The pancreas: it prompts insulin release when blood sugar is high, and reduces the release of glucagon, the hormone that raises blood sugar.
• The stomach: it slows the rate at which food moves on into the intestine.
• The brain: it acts on areas involved in appetite and fullness.

The natural hormone is short-lived. An enzyme called DPP-4 breaks it down within minutes, so it could never be used as a medicine as it is. The medications are engineered versions that last far longer.

What is a GLP-1 medication?

A GLP-1 medication, formally a GLP-1 receptor agonist, is a drug that binds to the same receptor as the hormone and switches on the same signals. The difference is how long it lasts: a day or a week, rather than minutes. Most are peptides closely modeled on GLP-1 and changed to resist breakdown. Tirzepatide is built on a second gut hormone, GIP, and acts on both the GIP and GLP-1 receptors, which is why it is called a dual agonist. Orforglipron, the newest, is a small molecule taken as a tablet.

How do GLP-1 medications work for weight loss?

GLP-1 is a natural regulator of appetite and calorie intake, with receptors in areas of the brain that control appetite. The medications act on those receptors, and slower stomach emptying adds to the sense of fullness after a meal. For weight management they are used together with a reduced-calorie diet and increased physical activity, not instead of them, and how much any one person responds varies.

How do they help with type 2 diabetes?

By prompting the pancreas to release insulin when blood sugar is raised and by reducing glucagon. That is how the class began: the first GLP-1 medication came into use for type 2 diabetes in 2005. Low blood sugar is a recognized risk when a GLP-1 is combined with insulin or a sulfonylurea, which is one reason a prescriber needs to know everything else you take.

How are GLP-1 medications taken?

Most are injections under the skin of the abdomen, thigh or upper arm, given with a pen or syringe once a week or once a day, depending on the medication. Two are tablets taken once a day: semaglutide and orforglipron. Treatment usually starts at a low dose and increases in steps, which gives the body time to adjust and is the main way side effects are kept manageable.

Which GLP-1 medications are there?

In the US: exenatide, liraglutide, dulaglutide, semaglutide, tirzepatide and orforglipron, plus lixisenatide in a combination with insulin. Semaglutide and tirzepatide are the most widely used.

What are GLP-1 medications used for?

Depending on the product, GLP-1 medications are prescribed for type 2 diabetes and for weight management, alongside diet and physical activity. Compounded preparations are not FDA-approved and have no approved use of their own.

What are the side effects?

Mostly digestive: nausea, diarrhea, vomiting, constipation, stomach pain and indigestion, most likely in the early weeks and after each dose increase. They have also been associated with thyroid C-cell tumors in rodents, and with pancreatitis, gallbladder disease and kidney injury from dehydration. Our guide to GLP-1 side effects covers each one, with the signs that need a clinician.

Who can take a GLP-1 medication?

The class is prescription-only and is not appropriate for everyone. It must not be used by anyone with a personal or family history of medullary thyroid carcinoma or Multiple Endocrine Neoplasia syndrome type 2, or after a serious allergic reaction to the medication, and weight-loss treatment is not recommended during pregnancy. Other conditions and medications need weighing, which is why every request goes through a clinician rather than a checkout page.

If you are considering treatment, the first step is an assessment. A licensed clinician reviews it and decides whether a GLP-1 medication is appropriate, whether something else fits better, or whether treatment is not indicated at all.

Is a compounded GLP-1 the same thing?

Compounded semaglutide and compounded tirzepatide are prepared by licensed compounding pharmacies for an individual patient on a clinician's prescription. Compounded medications are not FDA-approved and are not reviewed by the FDA for safety, effectiveness, or quality. Our guide to compounded GLP-1 medications explains what that difference means in practice.

GLP-2, peptides and supplements: the terms that get confused

GLP-2 is a different hormone from the same gut cells, with a different job, and is not a newer GLP-1. 'GLP-1 inhibitor' is usually a mix-up with DPP-4 inhibitors, a separate class of diabetes tablets. GLP-1 is a peptide, which is why most of the medications are injected. And products sold over the counter as 'GLP-1 supplements' are not GLP-1 medications. Each has its own article in our GLP-1 basics guide.

This article is educational and is not a substitute for personalized medical advice. Whether any medication is appropriate for you is a decision for a licensed clinician who has reviewed your health history.