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Prescription Weight Loss Drugs

Keeping your weight in check sometimes can be a lifelong challenge. Following a healthy diet and staying physically active can help. So can prescription drugs.

Weight loss drugs may be an option for you if have obesity, which is defined as a body mass index (BMI) of 30 or higher. For an adult who is  5 foot 8 inches tall, that’s a weight of 197 pounds or more.

Your doctor also may prescribe the drugs if your BMI is at least 27 and you have one or more weight-related health conditions, such as diabetes or high blood pressure.

Many people lose significant amount of weight with the medications. Others lose less or very little.

The medication semaglutide (Wegovy) received FDA approval for the treatment of obesity in 2021. Then in November 2023, the FDA approved a second drug as a treatment for obesity alone. That drug, tirzepatide, is sold under the brand name Zepbound. Tirzepatide is already available under a different name, Mounjaro, which is approved as a diabetes treatment but is prescribed off-label for weight loss.

Other types of older prescription weight loss drugs include liraglutide (Saxenda), naltrexone-bupropion (Contrave), orlistat (Alli, Xenical), and phentermine-topiramate (Qsymia).

Before you get a weight loss drug prescription, tell your doctor about your medical history. That includes any allergies or other conditions you have; medicines or supplements you take (even if they’re herbal or natural); and whether you’re pregnant, breastfeeding, or planning to get pregnant soon. 

How it works: Liraglutide is the same drug as the type 2 diabetes drugs Sadenxa and Victoza. It mimics an intestinal hormone that tells the brain your stomach is full.

Approved for long-term use? Yes.

Side effects: Nausea, vomiting, diarrhea, constipation, and low blood pressure. Serious side effects can include raised heart rate, pancreatitis, gallbladder disease, kidney problems, and suicidal thoughts. Liraglutide has been shown in studies to cause thyroid tumors in animals, but it is not yet known if it can cause thyroid cancer in humans.

What else you should know: If you don’t lose 4% of your weight after 16 weeks of taking liraglutide, your doctor may tell you to stop taking it because it’s unlikely to work for you, the FDA says.

How it works: Contrave is a combination of two FDA-approved drugs, naltrexone, and bupropion, in an extended-release formula. Naltrexone is approved to treat alcohol and opioid dependence. Bupropion is approved to treat depression and seasonal affective disorder and help people stop smoking.

Approved for long-term use? Yes.

Side effects: The most common side effects include nausea, constipation, headache, vomiting, dizziness, insomnia, and dry mouth. Contrave has a boxed warning about the increased risk of suicidal thoughts and behaviors associated with bupropion. The warning also notes that serious neuropsychiatric issues linked to bupropion have been reported. Contrave can cause seizures and must not be used in patients who have seizure disorders. The drug can also increase blood pressure and heart rate.

What else you should know: If you don’t lose 5% of your weight after 12 weeks of taking Contrave, your doctor may tell you to stop taking it because it’s unlikely to work for you, the FDA says. Contrave appears to signal the brain to lower the appetite.

How it works: Blocks your body from absorbing about a third of the fat you eat.

When a doctor prescribes orlistat, it’s called Xenical. If you get it without a prescription, it’s called Alli, which has half of Xenical’s dose.

Approved for long-term use? Yes.

Side effects include abdominal cramping, passing gas, leaking oily stool, having more bowel movements, and not being able to control bowel movements.

These side effects are generally mild and temporary. But they may get worse if you eat high-fat foods.

Rare cases of severe liver injury have been reported in people taking orlistat, but it’s not certain that the drug caused those problems.

What else you should know: You should be on a low-fat diet (less than 30% of your daily calories from fat) before taking orlistat.

Also, take a multivitamin at least 2 hours before or after taking orlistat because the drug temporarily makes it harder for your body to absorb vitamins A, D, E, and K.

Orlistat is the only drug of its kind that’s approved in the U.S. All other prescription weight loss drugs curb your appetite.

How it works: Curbs your appetite.

Your doctor may prescribe this under the names including Adipex or Suprenza.

Approved for long-term use? No. It’s approved for short-term use (a few weeks) only.

Side effects can be serious, such as raising your blood pressure or causing heart palpitations, restlessness, dizziness, tremor, insomnia, shortness of breath, chest pain, and trouble doing activities you’ve been able to do. Less serious side effects include dry mouth, unpleasant taste, diarrhea, constipation, and vomiting.

As with some other appetite suppressants, there’s a risk of becoming dependent upon the drug.

Don’t take it late in the evening, as it may cause insomnia.

If you take insulin for diabetes, let your doctor know before you take phentermine, as you may need to adjust your insulin dose.

You should not take phentermine if you have a history of heart disease, stroke, congestive heart failure, or uncontrolled high blood pressure. You also shouldn’t take it if you have glaucoma, hyperthyroidism, or a history of drug abuse, or if you are pregnant or nursing.

What else you should know: Phentermine is an amphetamine. Because of the risk of addiction or abuse, such stimulant drugs are “controlled substances,” which means they need a special type of prescription. Other drugs similar to phentermine that may be an option include benzphetamine, diethylpropion, and phendimetrazine.

How it works: Curbs your appetite.

Qsymia combines phentermine with the seizure/migraine drug topiramate. Topiramate causes weight loss in several ways, including helping you feel full, making foods taste less appealing, and burning more calories.

Approved for long-term use? Yes. Qsymia has much lower amounts of phentermine and topiramate than when these drugs are given alone.

Side effects: The most common side effects are tingling hands and feet, dizziness, altered sense of taste, insomnia, constipation, and dry mouth.

Serious side effects include certain birth defects (cleft lip and cleft palate), faster heart rate, suicidal thoughts or actions, and eye problems that could lead to permanent vision loss if not treated.

Women who might become pregnant should get a pregnancy test before taking Qsymia and should use birth control and get monthly pregnancy tests while on the drug.

You also shouldn’t take Qsymia if you have glaucoma, hyperthyroidism, heart disease, or stroke. Get regular checks of your heart when starting the drug or increasing the dose.

What else you should know: If you don’t lose at least 3% of your weightafter 12 weeks on Qsymia, the FDA recommends that you stop taking it or that your doctor increase your dose for the next 12 weeks — and if that doesn’t work, you should gradually stop taking it.

How it works: Semaglutide imitates an intestinal hormone that stimulates insulin production, lowering your appetite and making you feel full.

Semaglutide was initially approved as a treatment of type 2 diabetes and is prescribed for that use under the names Ozempic and Rybelsus. As Wegovy, it is specifically for treatment of obesity.

Approved for long-term use? Yes.

Side effects: Abdominal cramping, constipation, vomiting, passing gas, headache, fatigue, and heartburn. These side effects are generally mild and temporary.

In rare cases, issues involving the kidney as well as blurred vision have occurred. Semaglutide has been linked with instances of disease of the pancreas (pancreatitis). Get medical help right away if you develop symptoms of pancreatitis, including severe stomach or abdominal pain, or nausea/vomiting that doesn’t stop.

What else you should know: You would need to take semaglutide for life to manage your weight. Quitting it could lead to regaining most of the lost weight.

You should also follow a low-calorie diet and exercise program.

How it works: Mounjaro activates both the hormones GLP-1 and GIP receptors and leads to improved blood sugar control. During tirzepatide diabetes trials, researchers noted people who got tirzepatide lost much more weight than those on standard diabetes therapy.

Approved for long-term use? Not FDA-approved for weight loss but used to treat obesity off-label. 

Side effects: Nausea, vomiting, diarrhea, decreased appetite, constipation, upper abdominal discomfort, and abdominal pain.

What else you should know: This medication is given by injection under the skin once weekly.

How it works: Tirzepatide mimics two hormones, one that regulates insulin when your blood sugar rises and the other a gut hormone. Together, the molecules dampen your appetite so that you eat less. 

Approved for long term-use? Yes. Not approved for children.

Side effects: Nausea, diarrhea, vomiting, stomach pain, and constipation (trouble pooping). 

What else you should know: You take tirzepatide as a shot under your skin once a week. The dosage goes up over 4-20 weeks until you reach your target dose, which can be 5, 10, or 15 milligrams weekly.