Are weight-loss pills safe?

There’s a new class of medications that could potentially change the way the world thinks about obesity. Buzzy? Yes. Effective? Very. But are they safe? Here’s what you need to know.
Published March 6, 2023
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The very idea of a weight-loss pill can have the whiff of a snake oil salesman’s pitch—take this capsule and you’ll suddenly find it a lot easier to drop extra weight. But unlike some past weight-loss pills or random over-the-counter diet supplements, the current FDA-approved options can actually deliver on that promise. Combined with lifestyle changes, these medicines can help people maintain their weight loss, with some reportedly helping patients lose an average of 15% of their weight at 68 weeks. But as the buzz around how well they work has grown, so has confusion over whether or not they’re safe. To find the facts, we turned to experts.

How do these weight-loss medications work?

Most FDA-approved weight-management medications (both pills as well as injections) work by targeting your brain communication pathways. “They help reduce appetite by altering the signaling that regulates hunger, fullness, and cravings,” says Dr. Robert F. Kushner, M.D., professor of medicine in endocrinology and medical education at Northwestern University Feinberg School of Medicine in Chicago.

These treatments can be a game-changer for someone whose biology is not functioning correctly due to the disease of obesity (excess fat tissue), and whose biology makes weight loss and maintaining the weight loss more challenging. “In order to lose weight, patients need to do all they can to consciously reduce their calorie intake,” says Tom Wadden, PhD, a psychologist and professor at University of Pennsylvania who studies obesity treatments. By reducing hunger and increasing fullness, these medications are able to help you do just that.

Potential dangers of diet pills and “weight-loss” supplements

FDA-approved weight-management medications are one thing, but pills or supplements you find on store shelves or the internet that claim to help you lose weight are something very different—because they don’t have to go through any strict testing. As a result, off-the-shelf supplements and remedies can have a much more questionable record. There are no other FDA-approved weight-loss medications available without a prescription. As a result, off-the-shelf supplements and remedies can have a much more questionable record. For one, there’s no telling whether they even work.

“Remember, if a product's claim sounds too good to be true—and can be shipped to you for just $19.99—it's not true,” says Wadden. “It's a breakthrough in marketing, not weight control.” And even though they might sound scientific, claiming they can increase metabolism, reduce your appetite, or “unlock insulin resistance,” says Kushner, “there are limited published studies that confirm these mechanisms.” In other words, there’s just no proof.

Plus, if you’re buying weight-loss supplements in the grocery store or online, you’re probably not running them by your healthcare provider. “You shouldn’t buy medications online and start them without consulting with your healthcare provider,” says Wadden. After all, “you wouldn't treat your diabetes or hypertension that way.”

Finally, they can be just plain dangerous. “Dietary supplements and other OTC products can have adverse health effects,” Wadden says. For example, Ephedra was banned in 2004 because it can raise your risk of heart attack or stroke and Hydroxycut was pulled from shelves in 2009 after being linked to acute liver injury, cardiac arrhythmias, and ulcerative colitis. The FDA even maintains a list of currently available weight-loss supplements that contain hidden ingredients, including drugs that have been previously pulled from the market due to safety concerns.

Remember, since the dietary supplement industry is loosely regulated —the FDA considers them a food, not a drug—it’s hard to tell exactly how safe they are.

Whatever happened to Fen-Phen?

While the FDA does its best to only approve safe medications, it isn’t a guarantee that a drug can’t be dangerous. Fen-Phen, for instance, was an effective weight-loss drug combo that was linked to heart-valve damage and pulmonary hypertension, and eventually pulled from the shelves in 1997. The issue came down to the fact that it was used off-label. Both fenfluramine (the “fen” part of the drug) and phentermine (“phen”) were found to be safe when studied separately, but they’d never been tested for safety together. The medications currently approved for medical weight management, however, were all tested in their existing combinations.

Much more recent was Belviq, which the FDA withdrew from the market just a few years ago in 2020, citing an increased risk of cancer. And indeed, a systematic review concluded that those who took lorcaserin (the primary active ingredient in Belviq) had a higher risk of lung and pancreatic cancers. The extra safety study on Belviq was a requirement of the FDA when they approved the drug, showing they had concerns from the beginning.

The best (and safest) ways to lose weight

An FDA-approved weight-management medication can be helpful if you’re the right candidate for it. “All weight-management medications are approved for individuals with a body mass index of 30 or more, or a BMI of 27 or more with an associated medical problem,” says Kushner. “In addition, it is important to follow a healthy diet and be as physically active as possible since these are foundational behaviors for weight loss and improved health.” Remember: The goal isn't to hit a certain number on the scale, it's to work towards true weight health, which is finding the weight that has the best impact on your overall health and qualify of life.

That said, a weight-management medication shouldn’t be your first option when you decide to lose weight. Unless you have severe obesity disease, “patients should have tried six to 12 months in a formal lifestyle-modification program, such as WeightWatchers®, before starting a medication,” says Wadden. And it’s best to continue on with a lifestyle-modification program once you start the medication too.

Part of the reason a structured program is so helpful is because it can offer both critical education and greater emphasis on eating a healthy diet and ramping up physical activity—which you can’t learn or make a habit by taking medication. “We consider obesity to be a chronic disease similar to diabetes and hypertension,” says Kushner. “You don’t want a quick fix, but rather a long-term approach to a chronic condition.”

The bottom line

Aside from FDA-approved weight-management medications that have been okayed for you to use by your medical provider, weight-loss pills are best avoided. “All of the other over-the-counter options are dietary supplements that are not held to the same rigorous standards as medications,” Kushner says. “There is a dearth of information regarding their use, effectiveness, and safety—and in general are not recommended in the treatment of obesity.”

This content is for informational purposes only and does not constitute medical advice, diagnosis or treatment. It should not be regarded as a substitute for guidance from your healthcare provider.