Do weight-loss pills work?

It’s the question on so many minds. But the answer lies in another question: Are the pills that are most reliable available over-the-counter or by prescription? Experts, take it away.
Published March 6, 2023

Weight-loss pills. The phrase smacks of diet-culture from the era of late-night infomercials. But a new generation of medications to treat obesity has taken hold on TikTok and other social media. And these novel drugs are backed by actual science and prescribed by actual doctors. But do they live up to their hype in real life? We tapped a few experts for their take on what weight-loss medications can and can't do.

Are all weight-loss pills created equal?

There are two main groups of weight-loss pills: those you get through a healthcare provider (prescription anti-obesity medications) and those you buy without a prescription (supplements, including diet pills). There’s a canyon of a difference between them.

Dietary weight-loss supplements and diet pills (the kind you get without a prescription) have been around for decades, but they aren’t regulated by the FDA, meaning they aren’t tested for safety or efficacy. This counts for so-called natural supplements that claim to rev your metabolism. (Think raspberry ketones and apple cider vinegar pills.) And the same is true for more clinical-seeming ones that contain ingredients with strong biological effects. Take Hydroxycut. This popular supplement, which touted celebrity spokespeople and sleek magazine ads, was pulled from shelves in 2009 after numerous reports of liver damage and even death.

Now, on the complete other side of the universe—we’re talking a galaxy far, far away—are what’s known as anti-obesity medications, which need to prove their efficacy and safety to the FDA, and are only available via prescription. What’s more, they exist to treat an actual chronic health condition—like obesity—not to simply help someone shed a few pounds.

“We are getting a better understanding of the complex factors that influence obesity,” says Diana M. Plata, M.D., an obesity and sleep medicine physician for Northwest Community Healthcare in Arlington Heights, Illinois. “More importantly, the treatment options are expanding which is very encouraging to those living with obesity.”

Obesity drugs work by either suppressing appetite—reducing cravings and increasing feelings of fullness—or by decreasing the body’s ability to absorb and store fat from food.

9 medications FDA- approved for weight loss

While the following medications—which include both pills and injections—have been put through the paces research-wise, they aren’t a magic cure for everyone, and many come with side effects.


The FDA has approved the following four drugs for short-term use because they are stimulants classified as schedule III or IV drugs and may lead to dependency. They all work in a similar way, stimulating the central nervous system to suppress appetite:

  • phendimetrazine (Bontril)
  • diethylpropion (Tenuate)
  • benzphetamine (Didrex)
  • phentermine (Adipex-P, Fastin)

Long-term medications:

  • Orlistat (Xenical, Alli) is a gastrointestinal lipase inhibitor, meaning it inhibits the absorption of dietary fats.
  • Phentermine/topiramate (Qsymia) is a stimulant combined with an anti-seizure medicine that suppresses appetite by calming excitable nerve cells in the brain.
  • Naltrexone/bupropion (Contrave) combines an antidepressant (Bupropion) which suppresses appetite with hormone-impacting Naltrexone to help control food cravings.
  • Liraglutide (Saxenda) is a synthetic version of a hormone, known as glucagon-like-peptide (GLP-1), that is naturally found in your body and increases feeling of fullness.
  • Semaglutide (Wegovy) is a once-a-week injection that curbs appetite and delays gastric emptying so you feel fuller for longer.

Some antidepressant, diabetes, and anti-seizure medicines are occasionally prescribed to possibly promote weight loss. This is considered an “off-label” purpose, meaning for another use than originally designed.

What do you need to know about anti-obesity medications?

  1. They can work. Studies have shown that people who take anti-obesity medications lose weight from the start, says Robert F. Kushner, M.D., a professor of medicine and medical education at Northwestern University Feinberg School of Medicine and Medical Director of the Wellness Institute at Northwestern Memorial Hospital in Chicago. The rate of weight loss will vary from one person to another, but research has found that you can expect to lose about 5-15% of your weight in the first six months of treatment.
  2. They don’t work alone. Experts overwhelmingly recommend the use of these medications in tandem with a lifestyle modification program, like WeightWatchers, which encompasses eating a healthier diet, exercise, and behavior change techniques. This helps promote optimal weight management and overall health over the short- and long-term.
  3. They can improve your health. While 5% weight loss might not seem substantial—this means 10 pounds for someone who weighs 200 pounds—research links this amount of weight loss to a lower risk for diabetes, healthier cholesterol levels, less chronic inflammation, and more. (Here’s what 5% looks like on bodies of different sizes.)
  4. They require regular check-ups. Also know that you aren’t just prescribed a weight-loss medication and sent on your way. You’re seen regularly by your doctor and after three months of treatment, your healthcare provider will likely review your progress to determine whether you’re responding to the medication, Kushner says. "If not, we may stop the medication and consider an alternative medicine or approach.”

Who is a candidate for anti-obesity medications?

Most healthcare providers consider discussing weight-loss medications if your weight is impacting your health. The medication will be prescribed in combination with a program like WeightWatchers that promotes behavior interventions such as eating differently and increasing physical activity. As a general rule, anti-obesity medications might be an option if:

  • You have a body mass index (BMI) of 30+
  • You have a BMI of 27+ as well as certain qualifying health conditions, such as high blood pressure, type 2 diabetes, or sleep apnea

Body mass index (BMI), by the way, is one way to get a proxy of excess levels of fat by looking at a person’s weight in kilograms divided by the square of height in meters. A “healthy” weight is defined as a BMI of >18.5 to 24.9. “Overweight” is defined as a BMI between 25 to 29.9, and “obesity” kicks in at 30. (Find your BMI here.) Since BMI does not account for muscle mass, doesn’t distinguish health risks between men and women or different ethnicities and races, and overlooks other important health biometrics like blood sugars and cholesterol, it’s a far-from-perfect measurement system. But it’s the standard, so it’s what medical professionals use for now to screen for obesity and start the conversation.

In nearly all cases, regardless of BMI, kids and pregnant people should steer clear of all weight-loss medications since clinical trials do not include these populations, and as such, scientists cannot validate their safety.

How long do people take anti-obesity medications?

Obesity is a chronic disease, and like diabetes and hypertension it requires lifelong management. With the exception of phentermine, phendimetrazine, diethylpropion, and benzphetamine, anti-obesity medications are FDA-approved for long-term use, as they help address a dysfunction of the weight regulation system.

“All of the effects of the medication—like reduced hunger, increased fullness, or less cravings—are likely to return once the medication is stopped,” says Kushner. As a result, research shows that when the medications are stopped, weight regain occurs.

So, even after you've reached—and maintained—your health and weight goals, it’s important to discuss your individual situation with your healthcare provider before stopping your medication.

Bottom line

While supplements and over-the-counter weight loss pills aren’t effective or safe, FDA-approved medication can be good for people who fit the criteria. And they can work.

Think of anti-obesity medication as one step on a staircase that leads to long-term weight loss and maintenance. Weight loss can be challenging, but these medications help support the changes you are making in your life for a healthy you.

To find the most success, you’ll need to combine an anti-obesity medication with a healthy lifestyle, including regular activity, a balanced diet, stress management, healthy sleep habits, and social support. WeightWatchers can help you by offering accountability and guidance along the way.