GLP-1 drugs are a class of medications that mimic a natural gut hormone called glucagon-like peptide-1, which your body releases after eating to help regulate blood sugar, appetite, and digestion. Originally developed for type 2 diabetes, they’ve become some of the most prescribed medications in the world after clinical trials showed they also produce significant weight loss, with newer versions helping people lose 14% to 20% of their body weight.
How GLP-1 Drugs Work in Your Body
After you eat a meal, your intestines naturally release GLP-1. This hormone does three things at once: it signals your pancreas to produce more insulin (which lowers blood sugar), it tells your pancreas to stop releasing glucagon (a hormone that raises blood sugar), and it slows down how quickly food leaves your stomach. The net effect is steadier blood sugar and a longer-lasting feeling of fullness after eating.
The problem is that natural GLP-1 breaks down in your bloodstream within minutes. GLP-1 drugs are synthetic versions engineered to last much longer, from hours to an entire week depending on the formulation. They bind to the same receptors as the natural hormone but keep working continuously, which produces far stronger effects on blood sugar control, appetite, and the speed of digestion. That persistent suppression of appetite is a major reason people eat less and lose weight on these medications.
Available GLP-1 Medications
Several GLP-1 drugs are currently on the market, often sold under different brand names depending on whether they’re prescribed for diabetes or weight management.
- Semaglutide is the most widely recognized. It’s sold as Ozempic for type 2 diabetes and Wegovy for weight loss. Both are once-weekly injections. An oral tablet version also exists. Wegovy is approved for adults and children aged 12 and older with obesity, or for adults with a BMI of 27 or higher who have weight-related health problems. It also carries an approval to reduce cardiovascular risk in people with known heart disease and excess weight.
- Tirzepatide works on two hormone pathways instead of one, targeting both GLP-1 and another incretin called GIP. It’s sold as Mounjaro for type 2 diabetes and Zepbound for weight loss, both as weekly injections. Zepbound is approved for adults with a BMI of 30 or higher, or 27 with weight-related conditions. It also has an approval for moderate to severe obstructive sleep apnea in adults with obesity.
- Liraglutide is an older, daily injection. It’s sold as Victoza for diabetes and Saxenda for weight loss. It’s approved for adults and children 12 and older with obesity. Because it requires daily dosing rather than weekly, it’s become less popular as newer options have arrived.
Weight Loss Results
The weight loss from these drugs varies by medication and dose, but the numbers from clinical trials are substantial. In a head-to-head trial published in the New England Journal of Medicine, people taking tirzepatide (Zepbound) lost an average of 20.2% of their body weight over 72 weeks, while those on semaglutide (Wegovy) lost 13.7%. For context, that means a person weighing 250 pounds could expect to lose roughly 34 to 50 pounds depending on the medication.
These results represent averages. Some people lose more, some less. The weight loss typically happens gradually over the first year of treatment, then plateaus. Most of the evidence also shows that weight tends to return if the medication is stopped, which is why these drugs are generally considered long-term treatments rather than short courses.
Blood Sugar Control for Type 2 Diabetes
GLP-1 drugs were designed for diabetes first, and they remain among the most effective options for lowering A1C, a measure of average blood sugar over two to three months. Across dozens of clinical trials, these medications typically reduce A1C by 1% to 1.8 percentage points, which is a clinically meaningful drop. Semaglutide consistently produces the largest reductions, lowering A1C by 1.5% to 1.8% in most studies. Older and shorter-acting options like lixisenatide tend to produce more modest reductions around 0.8% to 1.0%.
Long-acting formulations taken once weekly generally outperform shorter-acting versions taken once or twice daily, both for blood sugar control and for patient adherence. A weekly injection is simply easier to maintain as a routine.
Heart and Kidney Benefits
One of the more significant findings about GLP-1 drugs extends beyond blood sugar and weight. In a large clinical trial of people with type 2 diabetes and chronic kidney disease, semaglutide reduced the risk of major cardiovascular events (heart attack, stroke, or death from heart disease) by 18% compared to placebo. The same trial found a 24% lower risk of kidney disease progression in the semaglutide group. These results are part of why Wegovy now carries an FDA-approved indication for cardiovascular risk reduction, a distinction that goes well beyond its original weight loss approval.
Common Side Effects
Gastrointestinal issues are by far the most frequent side effects, and they’re directly related to how these drugs work. Slowing stomach emptying helps with appetite but also causes digestive discomfort, especially when starting treatment or increasing the dose.
In a large analysis across clinical studies, roughly 1 in 5 people on GLP-1 drugs experienced nausea (21.5%), making it the most common complaint. Diarrhea affected about 10.6% of patients, vomiting 9.1%, indigestion 8.7%, constipation 7.9%, and decreased appetite 5.5%. These side effects are most pronounced in the first few weeks and often improve as the body adjusts. Doctors typically start patients on a low dose and gradually increase it over several weeks specifically to minimize these symptoms.
Who Should Not Take Them
All GLP-1 drugs carry a boxed warning, the most serious type of FDA safety alert, related to thyroid cancer. In animal studies, these medications caused medullary thyroid cancer in rodents. While the relevance to humans isn’t fully established, the drugs are contraindicated in anyone with a personal or family history of medullary thyroid carcinoma or a rare genetic condition called multiple endocrine neoplasia syndrome type 2 (MEN 2). People with a history of pancreatitis should also discuss risks carefully before starting treatment.
How They’re Taken
Most GLP-1 drugs are given as subcutaneous injections, meaning a small needle delivers the medication just under the skin of the thigh, upper arm, or abdomen. The weekly injectable versions come in prefilled pens that patients use at home. You can take the injection at any time of day, with or without food.
Oral semaglutide is the main pill option, and it comes with stricter rules. You need to take it on an empty stomach with no more than 4 ounces of plain water, then wait at least 30 minutes before eating, drinking anything else, or taking other medications. Skipping these steps significantly reduces how much of the drug your body absorbs, which can weaken its effectiveness. For many people, the convenience of a once-weekly injection actually wins out over a daily pill with fasting requirements.