Drugs for weight loss like liraglutide (Saxenda, Victoza) have been around for years, with newer arrivals like semaglutide (Ozempic, Wegovy) and tirzepatide (Mounjaro, Zepbound) offering an even bigger boost when it comes to shedding pounds.

“We now have a generation of very effective weight loss drugs,” says Craig Primack, MD, an obesity medicine physician with Scottsdale Weight Loss Center in Scottsdale, Arizona.

Here’s what to know about how weight loss medications work, who they’re best for, potential side effects, and more.

What Are Prescription Weight Loss Medications?

Prescription weight loss medications can help you lose weight if lifestyle changes aren’t working on their own.

Prescription weight loss medications are only available through a healthcare provider, unlike over-the-counter supplements that claim to promote weight loss. And unlike those supplements, prescription weight loss drugs are evaluated by the U.S. Food and Drug Administration (FDA) and only get approved if research studies prove them to be both safe and effective.

How Do Weight Loss Medications Work?

Different weight loss drugs use different mechanisms to help you drop extra pounds.

They Suppress Appetite

GLP-1 receptor agonists, a drug class that includes semaglutide, tirzepatide, and liraglutide, mimic a hormone called GLP-1 that our bodies produce during and after meals. GLP-1 can signal a feeling of fullness (satiety) and suppress appetite by acting directly on neurotransmitters (chemical messengers) in the brain.

GLP-1 receptor agonists also slow down the emptying of your stomach, keeping you feeling full for longer. When you’re not so hungry, it’s easier to take in fewer calories, which can help you lose weight.

Other weight loss medications suppress appetite in different ways.

They Prevent Fat Absorption

Lipase inhibitors like orlistat (Xenical) prevent your body from absorbing the fat you eat.

When you take a lipase inhibitor, the medication binds to fat in your gastroinestinal tract and travels with it until it leaves your digestive system.

They Boost Your Metabolism

Metabolism describes the complex process that gives your body energy. Your metabolism may work faster or slower than average depending on your genetics. And a slower metabolism can often make it harder to lose weight.

Some prescription weight loss medications, such as setmelanotide (Imcivree), speed up your metabolism, helping you burn more calories and lose more pounds.

Who Are Weight Loss Medications For?

Weight loss medications work best for people who need to lose a significant amount of weight and are unable to do so through diet and exercise alone. These drugs are not appropriate for anyone looking to lose a quick 5 to 10 pounds.

“The FDA is very specific on who qualifies for these drugs,” Dr. Primack says. The criteria include a body mass index (BMI) at or above 30, or a BMI above 27 with weight-related comorbidities (like type 2 diabetes and high blood pressure).

People taking prescription weight loss medication can expect to lose about 7 to 22 pounds more than they would if they relied on a healthy diet and exercise routine alone, which can generally result in up to two pounds of weight loss per week.

People who opt to use weight loss medications should also be willing to use the medications alongside a healthy diet and active lifestyle.

Think of the elements that lead to weight loss as being like four legs of a chair: exercise, diet, an accountability plan, and medicine. “[With] all four legs on the ground, you have a pretty stable base to lose weight,” Primack says.

FDA-Approved Weight Loss Medications

The FDA has approved seven different kinds of prescription medication for weight loss.

Tirzepatide (Mounjaro, Zepbound)

Tirzepatide belongs in the GLP-1 medication family. It keeps you feeling fuller for longer, slows digestion, and lowers appetite.

Mounjaro is the brand of tirzepatide medication prescribed to patients with diabetes, and Zepbound is the brand prescribed to those who are overweight or have obesity.

Tirzepatide is taken as a weekly injection. Your healthcare provider may teach you how to use it at home, or you can go to their office for injections, in which a small needle is inserted just under the skin in the fatty areas of your stomach, thighs, or upper arm.

In one meta-analysis, researchers found that people taking tirzepatide lost 21 more pounds than those who didn’t take it.

Serious side effects like low blood sugar are rare. More often, people report gastrointestinal symptoms like nausea, vomiting, and diarrhea. Between 40 and 50 percent of people on tirzepatide have these side effects, depending on their dosage.

Semaglutide (Ozempic, Wegovy, Rybelsus)

The popular injectable medications Ozempic and Wegovy belong to the semaglutide family. They are essentially the same medication, except Wegovy has a slightly higher maximum dosage.

These drugs work by prompting the release of insulin, which manages your blood sugar levels. It also slows down stomach emptying, which helps you feel fuller, longer.

Ozempic and Wegovy must be injected into fatty areas once a week. A meta-analysis of over 3,500 people found that those who injected semaglutide had almost 12 percent more weight loss than who took a placebo.

Smaller studies suggest that Rybelsus, which is semaglutide in pill form, may not offer the same level of weight loss.

Common side effects of semaglutide are pretty mild, says Primack. Most commonly, they include nausea, vomiting, and diarrhea. Constipation may also occur, but it is rare.

In some cases, more serious side effects may arise, such as:

Stomach paralysis
Upper stomach pain
Swelling that makes it hard to breathe or swallow
Rapid heartbeat

If you experience these symptoms, contact your healthcare provider right away.

Liraglutide (Victoza, Saxenda)

Liraglutide works similarly to semaglutide. It regulates blood sugar by releasing the right amount of insulin and also slows down stomach emptying.

With a full stomach, it’s easier to eat less, which helps you lose weight.

You have to inject liraglutide into fatty tissue once a day. This is more frequent than other options. A meta-analysis of 12 studies showed people taking liraglutide lost about seven pounds more than those who took a placebo.

Another analysis suggests that liraglutide may work less well than semaglutide.

Common side effects include moderate nausea and diarrhea. Other less common side effects include:

Blood sugar changes
Headache
Heartburn
Constipation
Vomiting
Stomach pain
Increased feelings of depression
Mood changes

Phentermine-Topiramate (Qsymia)

A combination of phentermine and topiramate, Qsymia works by decreasing appetite and making you feel fuller for longer.

Qsymia comes as an extended-release pill. You take it in the morning, and its contents slowly release throughout the day. According to a meta-analysis of six studies, phentermine-topiramate offered an average weight loss from almost 8 to 18 pounds, depending on the dosage.

The most common side effects of Qsymia include:

Changes in taste
Tingling, itching, burning, or prickling in your extremities
Dry mouth
Trouble staying focused
Irritability
Dizziness
Constipation
Numbness
Headache

Naltrexone-Bupropion (Contrave)

Bupropion-naltrexone combines medications used for depression, quitting smoking, and substance and alcohol addiction.

These drugs work together within the brain to manipulate the brain’s hunger center and reward system, which helps control appetite and cravings.

Contrave comes as a capsule, and it usually follows an escalating schedule. That means you’ll take one pill in the morning for a week, then two a day the next week. After that, you may need to increase your dosage to two pills in the morning, then again at night. Your provider will give you details on your dose schedule.

A meta-analysis of 10 studies found people taking naltrexone-bupropion lost an average of 11 more pounds than those who took a placebo.

Most commonly, Contrave side effects include nausea and vomiting, constipation, and headache. Less often, people have reported dizziness and insomnia. More serious side effects include heart problems, thoughts of suicide, and seizures. Contrave’s manufacturers recommend keeping a low-fat diet around the time you take the medication to lessen your chance of seizures.

Orlistat (Xenical)

Orlistat prevents your intestines from absorbing some of the fat in the food you eat. Instead of being absorbed and stored by the body, the fat exits through your stool.

This medication comes in capsule form, which you take by mouth three times a day. You can take orlistat with each main meal that includes fat. Orlistat works well when taken during your meal or one hour afterward, but doses can be skipped with missed meals.

Orlistat’s weight loss benefits rank lower than the other options. In one large high-quality study of over 3,000 people, orlistat caused 2.4 percent weight loss after four years of taking it.

Most of orlistat’s side effects come from the retention of fats in your intestines. These include:

Fatty stools
Frequent bowel movements
Gassiness
Inability to hold in stool

You can avoid some of these effects by adding a fiber supplement to your diet.

Setmelanotide (Imcivree)

Setmelanotide belongs to a class of medications called melanocortin 4 (MC4) receptor agonists, which signal the brain to decrease appetite and increase metabolism.

This weight loss medication has only been approved by the FDA for people with certain genetic disorders.

Imcivree is not frequently prescribed, Primack says, because those genetic conditions are rare. “There are probably only a couple hundred people in the country who would need it,” Primack says. Taking setmelanotide typically involves an injection once every morning in the fatty areas of the stomach, thighs, or upper arms.

A small study found that 80 percent of people taking setmelanotide for severe obesity from one genetic disorder lost at least 10 percent of their body weight at the one-year mark, while 45 percent of those taking it for a different disorder lost 10 percent or more.

The most common side effects include nausea and skin reactions at the injection site.

Other, more serious side effects call for immediate medical attention. These include unexpected, frequent, or long-lasting erections for men and an increased libido for women.

Are Weight Loss Medications Right for You?

Before you start a prescription weight loss medication, your provider will want to know more about your health conditions, lifestyle habits, and weight loss goals. For example, you shouldn’t take weight loss drugs while pregnant or breastfeeding.

Other health conditions may also limit which weight loss medications you can take, including the following:

You may need to wait before starting weight loss if you have taken a kind of antidepressant called a monoamine oxidase inhibitor in the last 14 days. Opioids (narcotic pain medications), benzodiazepines, and some anti-seizure medicines can also interact negatively with these drugs.

What to Expect at a Weight Loss Consultation

At your first weight loss consultation with a healthcare provider, you will discuss your weight loss goals, daily routine, and medical history. Your provider may also ask how long you’ve been trying to lose weight.

With this information, your provider will work with you to craft a weight loss plan. This plan may incorporate weight loss medications, but it will also include:

They can also discuss the possibility of weight loss surgery in the future if needed.

Weight Loss Medications Don’t Work Alone

Your weight loss plan has to include other activities to work at its peak. All prescription weight loss medications work best alongside a healthy diet and ongoing exercise.

It can feel challenging to make big lifestyle changes, and it’s okay to ask for help. Your provider can direct you to experts like registered dietitians and nutritionists, as well as resources designed to help you get on track and stay there.

The Takeaway

When taken alongside a healthy diet and regular exercise, prescription weight loss medications can help you lose weight if lifestyle changes alone aren’t giving you the results you want.
Weight loss medications work by suppressing your appetite, curbing cravings, boosting your metabolism, or preventing your body from absorbing some of the fat you eat.
The FDA has approved seven types of prescription medication for weight loss, and your provider can help you decide which one may work best for you.

Sean Hashmi, MD

Medical Reviewer

Sean Hashmi, MD, is an experienced nephrologist and obesity medicine specialist based in Southern California. As the regional director for clinical nutrition and weight management at a prominent healthcare organization in Southern California, Dr. Hashmi oversees the development and implementation of cutting-edge nutritional programs and weight management strategies. With his innovative approach and unwavering commitment to providing evidence-based solutions, he is a highly sought-after speaker and a leader in his field.

Hashmi founded the nonprofit organization SelfPrinciple.org to provide accessible and accurate health, nutrition, and wellness information to the public. Through this platform, he shares the latest research findings, empowering individuals to make informed decisions about their well-being. Self Principle also supports children's education by providing scholarships, books, and supplies, so that students have the resources necessary to succeed academically and build a brighter future.

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Abby McCoy, RN

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Abby McCoy is an experienced registered nurse who has worked with adults and pediatric patients encompassing trauma, orthopedics, home care, transplant, and case management. She is a married mother of four and loves the circus — that is her home! She has family all over the world, and loves to travel as much as possible.

McCoy has written for publications like Remedy Health Media, Sleepopolis, and Expectful. She is passionate about health education and loves using her experience and knowledge in her writing.

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Prescription Weight Loss Medications

What Are Prescription Weight Loss Medications?