What is GLP-1? How they work, benefits & side effects

Glucagon-like peptide-1 receptor agonists, or GLP-1s, are a class of medications that started as a diabetes treatment and evolved into a popular weight loss option. They mimic GLP-1, a hormone that helps regulate blood sugar and appetite. Certain GLP-1 medications can also reduce cardiovascular or kidney complications 

GLP-1 is short for glucagon-like peptide-1. It is a type of hormone that cells in the intestines release after a person eats. Once in the bloodstream, GLP-1 can:

• Increase the release of insulin, a hormone that moves glucose (sugar) from the bloodstream into cells

• Reduce the release of glucagon, another hormone that works in tandem with insulin to help regulate blood sugar

• Slow gastric emptying, or the rate at which food moves from the stomach to the lower intestine

Research has established benefits beyond blood sugar control and weight management: Certain GLP-1-based medications are now approved to reduce cardiovascular or kidney complications in some people, while others are approved to treat obstructive sleep apnea or metabolic dysfunction-associated steatohepatitis (MASH).

“GLP-1 agonists are some of the most powerful medicines for weight management that we have to offer,” says Raoul Manalac, MD, Senior Director of Clinical Experience for Metabolic Health at Ro. 

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These medications work by mimicking the GLP-1 hormone and binding to GLP-1 receptors in the brain and gut, says Evan Nadler, MD, MBA, former co-director of the obesity program at Children’s National Hospital.

“In the brain, [GLP-1] is thought to reduce food intake by some element of appetite suppression,” Dr. Nadler says. “Lots of people describe it as decreasing ‘food noise,’ which means how much you think about food and how much you crave different foods.”

In the gut, GLP-1 slows the rate at which digested food empties from the stomach and moves through the digestive tract, Dr. Nadler adds. When food stays in the stomach, a person may feel full for longer, which can reduce overall food and calorie intake.

GLP-1 medications also help stimulate insulin release and reduce glucagon secretion, which helps regulate blood sugar levels.

GLP-1 medications may also reduce visceral fat — the type of fat that surrounds organs and can contribute to conditions such as type 2 diabetes, cardiovascular disease, and fatty liver disease.

A review of 30 randomized controlled trials, which included 1,736 adults with and without type 2 diabetes or fatty liver disease, found that treatment with GLP-1 agonists significantly reduced both visceral and liver fat.

Several GLP-1 medications are on the market. They are commonly prescribed for type 2 diabetes, weight loss, and other health conditions. There are several GLP-1-based medications, including those containing semaglutide, tirzepatide, orforglipron, liraglutide, and dulaglutide. They differ in how they're taken, their approved uses, and their effects on weight and blood sugar.

Semaglutide (Ozempic, Wegovy)

Semaglutide comes in two brand names, each available as a weekly injection and a daily pill, with different approved uses:

• Ozempic is approved to improve blood sugar control in adults with type 2 diabetes and to reduce the risk of heart attack, stroke, and kidney disease complications in certain adults with type 2 diabetes. It comes as a prefilled injection pen taken once a week or as a daily pill (previously marketed as Rybelsus).

• Wegovy comes as a weekly injection or a daily Wegovy pill. Both forms are approved for weight management in adults with obesity or overweight and a weight-related condition, and to reduce the risk of major cardiovascular events, such as heart attack or stroke, in adults with cardiovascular disease who have obesity or overweight. The pen is also approved for children ages 12 and up with obesity and for adults with metabolic dysfunction-associated steatohepatitis (MASH), a form of fatty liver disease.

Tirzepatide (Mounjaro, Zepbound)

Tirzepatide belongs to a different class of medications called dual-action GLP-1/GIP receptor agonists. It acts on two hormone receptors: GLP-1 and glucose-dependent insulinotropic polypeptide (GIP).In clinical trials, tirzepatide has produced greater average weight loss than some GLP-1-only medications, including semaglutide.

Tirzepatide is available as two brand-name medications:

• Mounjaro is approved to improve blood sugar control in adults and children ages 10 and older with type 2 diabetes, and to reduce the risk of major cardiovascular events in adults with type 2 diabetes at high risk for them. It comes in single-dose pens and vials, as well as multi-dose KwikPens and vials, and is injected once a week.

• Zepbound is approved for weight management in adults with obesity, or with overweight and at least one weight-related condition, and to treat moderate to severe obstructive sleep apnea in adults with obesity. Like Mounjaro, Zepbound comes in single-dose pens and vials, as well as multi-dose KwikPens and vials. It is injected once a week.

Orforglipron (Foundayo)

Orforglipron is an oral medication in the GLP-1 class that is approved for weight management. It is available under one brand name:

• Foundayo is approved for weight management in adults with obesity, or with overweight and at least one weight-related condition, such as high blood pressure. It is taken as a pill once a day, with or without food.

Liraglutide (Saxenda, Victoza)

Liraglutide was first approved to treat type 2 diabetes and later gained approval for weight management. It is available as a generic and under two brand names:

• Saxenda is approved for weight management in adults with obesity, adults with overweight and at least one weight-related condition, and children ages 12 and up with obesity who weigh more than 60 kg (about 132 pounds). Unlike the weekly injections, Saxenda is injected once a day.

• Victoza is approved to improve blood sugar control in adults and children ages 10 and older with type 2 diabetes. It also reduces the risk of major cardiovascular events, such as heart attack and stroke, in adults with type 2 diabetes and established cardiovascular disease. Victoza comes in a self-injectable pen taken once a day.

Dulaglutide (Trulicity)

Dulaglutide is another medication for type 2 diabetes. While it may promote some weight loss, it is not approved for that purpose. Dulaglutide is available under one brand name:

• Trulicity is approved for blood sugar control in adults and children ages 10 and older with type 2 diabetes. It is also approved to reduce the risk of major cardiovascular events (heart attack, stroke) in adults with type 2 diabetes who have established heart disease or multiple cardiovascular risk factors.

While all GLP-1 medications may promote some weight loss, four medications are specifically approved for chronic weight management:

• Zepbound (tirzepatide)

• Wegovy (semaglutide)

• Foundayo (orforglipron)

• Saxenda (liraglutide)

In clinical trials, people taking these medications have lost an average of roughly 5% to more than 20% of their starting body weight, depending on the medication, dose, treatment duration, and patient population.

• One clinical trial compared weekly semaglutide (Wegovy) with daily liraglutide (Saxenda). At 68 weeks, participants taking 2.4 mg of semaglutide lost 15.8% of their body weight, compared with 6.4% for participants taking 3 mg of liraglutide (how the two medications compare).

• In a 2024 trial of tirzepatide (Zepbound) for weight loss, participants lost an average of 20.9% of their body weight at 36 weeks.

• In a 2025 randomized clinical trial comparing tirzepatide and semaglutide in adults with obesity but without diabetes, participants taking tirzepatide lost an average of 20.2% of their body weight over 72 weeks, compared with 13.7% among those taking semaglutide.

Research suggests that Zepbound (tirzepatide) is the most effective weight loss medication currently available, based on a 2026 network meta-analysis of 262 trials.

The higher 7.2 mg dose of Wegovy (Wegovy HD) produced an average weight loss of 18.7% over 72 weeks in clinical trials. 

Every weight loss journey is unique. How much weight a person can lose on Zepbound or any other GLP-1 medication depends on a variety of factors, including starting weight, overall health, and lifestyle.

GLP-1 medications, whether injections or pills, are not meant to work in isolation. Healthcare providers typically recommend pairing them with lifestyle changes such as a balanced diet and regular exercise.

All FDA-approved GLP-1 medications went through an extensive clinical review and approval process. When  a healthcare provider determines that these drugs are the right fit for you and you use them as directed by a healthcare provider, they are considered generally safe. The most common side effects are gastrointestinal (GI) issues, which are often mild to moderate.

Common side effects of GLP-1 medications may include:

• Abdominal pain

• Constipation

• Diarrhea

• Nausea

• Heartburn

• Vomiting

• Fatigue

• Headache

Side effects may be more intense when a person first starts taking the medication, but they often ease over time. Starting at the lowest dose and increasing it gradually may help minimize side effects.

A healthcare provider can advise on the safe use of these medications and recommend ways to manage mild side effects, which may include:

• Eating smaller meals to help the body adjust to slower digestion

• Drinking more water to help prevent dehydration

• Getting more fiber to help with constipation

• Taking an anti-nausea medication, if a healthcare provider recommends one, to help with vomiting or queasiness

• Limiting large meals and avoiding certain foods, such as fatty or greasy, or foods, that can worsen digestive side effects

Rare but serious side effects and warnings 

GLP-1s  also carry warnings about potentially serious side effects and complications. Some have been observed in clinical trials or after approval, while the strength of evidence and risk vary by medication.

• Diabetic retinopathy complications. In people with type 2 diabetes, especially those with existing diabetic eye disease, rapid improvements in blood sugar may sometimes be linked  with eye problems.

• Gallbladder disease. Gallstones and gallbladder inflammation have been reported in some studies of these medications.

• Low blood sugar (hypoglycemia). People who take a GLP-1 medication along with a sulfonylurea or insulin to treat diabetes may have a higher risk of low blood sugar.

• Acute pancreatitis. Sudden inflammation of the pancreas may occur with these medications, though it is rare.

• Allergic reactions. Severe reactions — including anaphylaxis — can occur in people who are allergic to ingredients in GLP-1 medications.

• Thyroid tumors. Several GLP-1-based medications have caused thyroid C-cell tumors in animal studies, although it is unknown whether they cause these tumors in humans. 

• Gastroparesis. Some research suggests that GLP-1 medications may be linked to gastroparesis, or delayed stomach emptying, in some people.

• Kidney injury. Dehydration from severe nausea or vomiting may lead to acute kidney injury, which can require medical attention.

• Pulmonary aspiration during surgery. Taking GLP-1 medications may increase the risk of pulmonary aspiration during general anesthesia or deep sedation in some people. Tell your surgical and anesthesia team if you take one of these medications.

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Who should not take GLP-1 medications?

GLP-1 medications may not be suitable for everyone. Some medical conditions are contraindications meaning you can’t take the medication while others require additional precautions or assessment by your healthcare provider:

You should not take the GLP-1 medications if you:

• Have a personal or family history of medullary thyroid cancer or a condition called multiple endocrine neoplasia type 2 (MEN 2).

• Have had a serious allergic reaction to the medication or any of its ingredients.

Talk to your healthcare provider about additional risks and precautions if you:

• Are pregnant, planning to become pregnant, or breastfeeding

• Have a history of pancreatitis or severe gastroparesis

• Have severe gastroparesis, a condition that slows stomach emptying, since GLP-1 medications can further delay this process.

Your healthcare provider can review your medical history and determine whether a GLP-1 medication is appropriate for you.

You may be a good candidate for GLP-1 treatment if you:

• Have obesity, (generally defined for adults as a BMI of 30 or higher)

• Have overweight (a BMI of 27 to 29.9) plus at least one weight-related condition, such as heart disease or type 2 diabetes

• Have metabolic dysfunction-associated steatohepatitis (MASH) with moderate to advanced liver fibrosis 

• Have moderate to severe obstructive sleep apnea and obesity

Ultimately, the decision to start treatment for weight loss is up to you and your healthcare provider, who can review factors such as personal and family health history, current weight, and health conditions to determine whether GLP-1 therapy is suitable.

GLP-1 medications can be highly effective, but they can also be expensive. List prices can exceed $1,000 per month before insurance, savings cards, or other discounts.

Many plans cover GLP-1 medications for type 2 diabetes, but coverage for weight management is less consistent and often depends on the plan, so some people pay the cash price.

As of October 2026, the following are examples of manufacturer list prices and self-pay prices. Actual costs depend on the medication, dose, and eligibility for savings programs.:

• Zepbound single-dose pens: $1,086.37

• Zepbound KwikPens: $299–$449* (cash price, depending on dose)

• Mounjaro: $1,112.16

• Ozempic pen and pill: about $1,000

• Wegovy pen: $1,349.02 or $199–$399* (cash price)

• Wegovy pill: $1,349.02 or $149–$299* (cash price)

• Foundayo: $649 or $149–$299* (cash price)

• Saxenda: $1,349.02

• Generic liraglutide: $315 (average cash price; varies by pharmacy)

*Prices may reflect limited-time offers and are subject to change; see more here.

If insurance covers weight loss medications, manufacturer savings programs may help reduce costs. Pharmacy discount programs and coupons may also help offset cash prices. Telehealth providers such as Ro may help lower costs too, with cash prices starting at $149 per month for some medications and doses. Medication costs are separate from the Ro Body membership fee.

Talk to a healthcare provider, such as a provider on Ro, if you are interested in taking a GLP-1 medication for weight loss. A provider can evaluate whether you are a good candidate based on your goals, health, and personal and family health history.

Questions to ask before getting a prescription for a weight loss medication include:

• Which weight loss medication is most appropriate for me?

• How much weight can I expect to lose on the medication?

• What are the possible side effects?

• How do I manage side effects if I have them?

• Will my health insurance cover the cost?

• How might this medication interact with other medications I take?

• How will my progress and side effects be monitored while I am on the medication?

• What dietary changes should I make while taking the medication?

• What types of exercise should I do, and how often should I work out?

In a 2026 network meta-analysis of weight loss medications, tirzepatide, semaglutide, and orforglipron led to about 10–15 percentage points more weight loss at one year than lifestyle changes alone. By comparison, the older combination medication phentermine-topiramate (Qsymia) led to about 8 percentage points more.

“There are some older-generation drugs that are safe and effective and are still in use,” Dr. Nadler says. “When I talk to patients about weight management, I always bring up these other options as well, because some people don’t want to use a needle.”

The side effects of older medications also differ from those of GLP-1 medications. For example, phentermine can cause a rapid or irregular heart rate, high blood pressure, headache, and insomnia, while orlistat can cause gas, increased bowel movements, and fecal incontinence.

Older prescription weight loss pills include:

• Naltrexone-bupropion (Contrave)

• Orlistat (Xenical)

• Phentermine (Adipex-P, Lomaira, Suprenza)

• Phentermine/topiramate (Qsymia)

If a healthcare provider prescribes a GLP-1 medication, treatment will likely start at the lowest dose. For injectable medications, the provider may also show you how to administer your first injection.

In the first few weeks, you may experience mild side effects as your body adjusts to the medication. You may also begin to notice changes in your appetite and weight.

It can take time to see more substantial results. In one study of people with overweight or obesity who took semaglutide, participants lost an average of:

• About 15 pounds (about 6% of body weight) within three months, based on 175 participants

• About 27 pounds (about 11% of body weight) after six months, based on 102 participants

Recommended lifestyle changes during GLP-1 therapy

GLP-1 medications can support weight loss by increasing satiety and reducing food cravings. Healthcare providers typically recommend pairing treatment with lifestyle changes such as increased physical activity and a balanced, nutritious diet.

“These [medications] can help patients feel more full for longer or more full on less food,” Dr. Manalac says. “This can help patients feel more confident about making lifestyle changes — particularly dietary changes that play an important role in weight management.”

Monitoring and follow-up with a healthcare provider

While taking any of these medications, you will need regular monitoring from a healthcare provider.

When you first start treatment, your healthcare provider will work with you to adjust your medication dose. They will increase the dose gradually, a process called titration, until it is effective. After that, you will see your provider at regular intervals so they can monitor side effects and track your progress.

Considerations for long-term use

GLP-1 medications for weight loss are not a quick fix. They typically require long-term use to maintain results, and stopping these medications may lead to weight gain or issues with blood sugar control, even after successful long-term weight loss.

In one follow-up study of 327 adults with obesity or overweight plus at least one weight-related medical condition, those who stopped semaglutide treatment and lifestyle interventions regained about two-thirds of the weight they had lost within one year.

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GLP-1 medications can be effective tools for weight loss and blood sugar control. While they work in similar ways, key differences between medications may affect which one is a good option for you.

Talk with a healthcare provider about weight loss medications, how they work, and their potential risks. A provider can determine whether one might be a good fit based on your health history, weight management goals, and other factors.

• GLP-1 agonists can treat multiple health conditions. These medications were first approved to help regulate blood sugar in people with type 2 diabetes but were later found to promote weight loss, among other health benefits.

• All of these medications mimic the GLP-1 hormone, which helps to reduce appetite, make you feel full faster, and improve blood sugar control. Dual-action GLP-1/GIP receptor agonists such as Zepbound and Mounjaro (how the two compare) can also mimic the action of GIP, a hormone that helps regulate blood sugar levels and metabolism.

• GLP-1 medications have similar common side effects. The most common are GI issues such as nausea, vomiting, and constipation. These side effects tend to be mild and often ease the longer a person takes the medication.

• These medications are typically meant to be taken long term. Stopping them too soon may lead to regaining the weight lost.

• GLP-1 medications can cost more than $1,000 each month at list price, and many insurance plans do not cover them when they are prescribed for weight loss. Savings programs, coupons, and other discounts may help make them more affordable, and cash prices on Ro start at $149 per month* for some medications and doses.

*Prices may reflect limited-time offers and are subject to change; see more here.