Ozempic is great for weight loss — but losing muscle is a side effect to watch out for

We’re used to seeing Serena Williams on our TVs, muscles flexing, smashing a tennis ball past her opponent. But in a recent 30-second commercial, Williams traded the racket for a GLP-1 drug injector pen.

Williams, whose most recent child was born in 2023, has become a spokeswoman in her post-retirement days for Ro, one of the many boutique health care firms to get in on the GLP-1 craze. “They say GLP-1s for weight loss is a shortcut — it’s not. It’s science,” she says during the spot. “After kids, it’s the medicine my body needed.”

Here is one of the world’s greatest athletes, giving voice — in commercials running during primetime TV, on the Today show, and on social media — to a frustration that many people have felt. She gained weight after she had kids. And even though, in her words, she was “doing everything right” after the pregnancy, she couldn’t cut as much weight as she liked. That’s where the GLP-1 drug came in and delivered results: Williams lost 31 pounds.

But there’s just one problem with the pitch: GLP-1 drugs like Ozempic and Wegovy are, in some ways, a shortcut.

“Americans always want the fucking pill,” Dr. Robert Lustig, a metabolic scientist at the University of California-San Francisco, told me. “I view GLP-1s like a Band-Aid. … There’s nothing wrong with a Band-Aid. But what if you didn’t clean your wound and you just put the Band-Aid on? The Band-Aid is necessary, but it’s not sufficient.”

The consequences of patients slapping on the Band-Aid — taking a GLP-1 — without treating the underlying issue with the kind of healthy eating and exercise that are still necessary even with these drugs is becoming clear. Scientists have found that some GLP-1 patients can lose significant muscle mass, as well as a loss of functional strength, due to a lack of energy. Rather than feel fitter and ready to go out in the world or onto the tennis court, these are patients who find walking up the stairs to be almost debilitating.

For this story, I sought to understand how this is playing out in American culture. In searching Reddit communities dedicated to GLP-1 drugs, I found lots of normal people whose experience backed up that research: They had long tried to lose weight but could never quite meet their goals — until they went on a GLP-1 drug.

But even as they lost weight, they didn’t feel better. Some of them felt worse, weaker. There are dozens of posts of GLP-1 patients coming to their peers, asking for advice about workouts they could do to stem the muscle loss. A few hope to find the right diet that will allow them to feel energetic and avoid muscle loss while losing the weight — but without having to commit to strength training that needs to go along with it.

While the term “strength training” may conjure images of ripped bodybuilders, doctors increasingly emphasize the importance of muscle training for all of their patients, from the 30-year-old marathon runner to the 65-year-old retiree. That’s because research has shown that more lean muscle helps you age better and protects against hazards, such as falls, that pose a greater and greater threat as you get older.

These drugs are already wildly popular, and their use is likely to keep growing. In November, the Trump administration struck deals with Lilly and Novo Nordisk to lower the cash price of their drugs in exchange for expanded Medicare coverage. Those price changes, which will begin to take effect next year, could further grow the number of Americans taking these medications, including among seniors for whom any loss of muscle mass is a serious health concern. One quarter of GLP-1 prescriptions dispensed in 2024 were for people older than 65.

Falls are already one of the most potent killers of older adults; more than 40,000 Americans over 65 died from falls in 2023, and the death rate has tripled since 1990. If more patients start taking semaglutide for its effects on cognition, for example, and fail to eat and exercise properly, they could experience malnourishment and significant muscle loss; both could put their long-term health at risk.

That doesn’t mean GLP-1 drugs are a bad deal for public health. On the population level, obesity is associated with a host of major ills, and Americans have long been desperate to lose weight. The class of drugs that includes Ozempic, Wegovy, Mounjaro, and now countless others — Zepbound, compound GLP-1s, etc. — are the most impressive weight-loss tools we’ve ever seen. They work because they slow digestion and tell your brain you’re full, which makes it easier for people to eat less. While these treatments are still fairly new, observational studies have found that patients who stay on these drugs for a year or more can lose 10 percent of their body weight on average. And on the population level, obesity rates are already starting to decline.

Scientists are also discovering that these drugs have amazing potential to treat a breadth of issues: from addressing substance-abuse disorders, lowering your risk for heart disease, and even potentially preventing dementia and Alzheimer’s disease. Recent studies have found that taking a GLP-1 like Wegovy or Ozempic is even associated with lower cancer deaths.

But to stem the risk of muscle-mass loss, you must also be willing to commit to improving your diet and adopting a serious workout regimen over the long term. GLP-1 drugs may be magical when it comes to weight loss, but they are not magic pills. Which means that along with the rise of Ozempic and other GLP-1s is a coming reckoning over America’s shortcut culture.

“Is this just a necessary evil to weight loss?”

Plenty of athletes who are not world-famous see the same appeal in GLP-1 drugs that Serena Williams did.

One person in particular stood out to me. A self-identified weight lifter, CrossFit enthusiast, and horse rider, who I’ll call Sam, shared their experience on Reddit. They explained they had always struggled to lose weight despite strict meal preparation and eating a lot of protein.

And so, Sam started taking Wegovy. ”I’m happy with the results,” they said — before getting to a pretty big caveat for somebody who’s always had an active life.

Despite aiming to eat 100 grams of protein every day, they said they were feeling weak. “I swear I can feel my muscle being broken down. Is this a thing??” Sam asked in the online forum. “I actually feel less firm, more wobbly and flabby. I seem to have less definition,“ they said. “Is this just a necessary evil to weight loss?”

The internet is filled with examples just like this. “Anyone else having a hard time working out on Wegovy?” asked one Reddit poster last year. They even felt their arms were weaker while bowling. Another person realized something was wrong when they could no longer do yard work around the house. Other people have noticed leg weakness after light walking or climbing the stairs: “I actually struggle to go up a staircase and I’m only 32,” said one GLP-1 patient.

“I know a lot of people are working out, and I do need to begin exercising on top of the wegovy, but I’m just wondering if anyone else is experiencing extreme weakness or if it’s just me and my un-toned self,” they asked.

Sam’s post in particular had a lot of comments, with one respondent even urging the patient to reconsider: You are “a strong, capable goddess. You don’t need to lose weight.” Accept who you are. In response, Sam laid out the dilemma that so many people who have sought to lose weight over the years face: “Unfortunately, some of us just do NOT lose weight with diet and exercise.”

It’s true: Weight loss is not assured from diet and exercise. Some people have a genetic disposition to becoming obese. And not everybody who is obese is unhealthy; the body mass index is an imperfect measurement, and some people who are technically obese can still be healthy if much of their weight is muscle. Still, the realization that obesity is a disease to be treated, rather than a personal failure that can only be remedied through personal growth, has been important in reducing the prejudices that overweight people have long faced.

But at the same time, it is a slippery slope from acknowledging diet and exercise may not be sufficient on their own to thinking a drug like Ozempic can make them unnecessary. Some people, like Sam, have always exercised and viewed GLP-1s as an extra push to help them reach their weight goals. But I also encountered other people who did not necessarily have healthy habits before but were able with the drugs to cut weight for the first time. One patient on Reddit acknowledged that they don’t work out and they don’t adhere to a particular diet. They have been losing weight, but they are “scared” about losing too much weight — so they ask if they can just eat more chicken or drink a protein shake and regain the muscle “without working out.”

They have reason for concern: The same clinical trials that have shown how effective GLP-1 drugs are with weight loss have also consistently reported muscle loss or weakness among patients. When one group of researchers evaluated the type of body mass that patients on semaglutide drugs were losing, they found that about 40 percent was important muscle.

The GLP-1 market is only going to grow as the drugs prove useful for a wide array of treatments. People, including those who are not overweight, may take them preventively to stave off cardiovascular disease or dementia. For them, people who are already at a healthy weight, muscle loss is an even more serious concern. If GLP-1 drugs do prove to be promising for treating age-related cognitive decline, for example, then appropriate diet and exercise will be even more paramount for that patient population. The last thing we want is more seniors suffering catastrophic injuries during a fall because of lost muscle mass.

But understanding what exactly is causing the muscle loss is important. Scientists are still figuring that out, but early indications are that the cause is not the drugs themselves, then some of the lifestyle changes the drugs can lead to..

One study from researchers at the University of Utah suggests the loss of strength is largely the result of not eating enough calories. In their research on mice, they found less muscle mass loss than expected. Instead, after taking a GLP-1, mice were losing their functional strength — how much they could lift or move around — even when muscle size stayed the same. In other words, the mice appeared weaker even though their muscle mass hadn’t changed.

“Strength is not just a factor of how much muscle you have, but whether you can move that muscle effectively. There’s an energetic component to it,” lead author Katsu Funai told me. The animals on a GLP-1 drug may have had less energy because they were eating less — and therefore they wouldn’t be able to exert as much force with their muscles. It’s not the GLP-1s per se; it’s what the GLP-1s lead to without intervention.

The findings could inform how we prescribe Ozempic, Funai said: Smaller doses might help to mitigate the loss of functional strength. Otherwise, losing weight too quickly is going to mean losing energy quickly — and therefore feeling weaker. In the excitement over Ozempic, and the potential to lose a lot of weight and fast, people seem to have forgotten a fundamental truth about weight loss: “More is not necessarily better,” Funai said.

Before GLP-1 drugs existed at all, dieticians urged their patients to pace weight loss — no more than 1-2 pounds per week — for exactly this reason: You don’t want to end up malnourished and weakened. With a conventional diet, that can often lead to you eating more, which in turn eliminates the weight loss. But when your appetite is suppressed by GLP-1s, the weight loss can continue, and with it, strength and energy loss.

“With these GLP-1s, that conversation [about diet and exercise] has been sidelined,” Funai said. “There are nuances to these things that I think are being missed not just from the public, but also from scientists,”

How to make the most of GLP-1s

Ironically, the very problem that GLP-1s were meant to overcome — that many Americans simply struggle to eat right and exercise enough — remains just as central even with the drugs.

And many of the people taking GLP-1s are starting at a disadvantage: Only 49 percent of Americans say they are extremely or very confident that they know what a healthy diet looks like, and about twice as many say they should get more exercise.

If your sole goal is to lose weight, a GLP-1 alone could get you there — but not in the healthiest way. Unless you change what you eat, you’re still putting the same junk in your body — albeit less of it — with the same or more negative effects on your energy and stamina.

“If you don’t change your behavior, if you don’t change your habits, you may be looking good, you may be losing weight, but metabolically, your body is in turmoil,” said Nayan Patel, a pharmacist who works with patients taking the drugs. “We’ve got to use these drugs in the right manner.”

So what should people on GLP-1s aim to eat? A high-protein diet delivering a lot of amino acids is important, Patel said: Eggs, nuts, lentils, poultry, and fish are all good sources. You can cut down on the carbs and sugars; your body won’t need them to produce energy because you’ll be cutting fat. Eating protein and strength training allows your body to be more effective at trimming the fat, without compromising your core strength.

Like anything hard but worth doing, there’s a lot to overcome. Many Americans have become intimidated by gym culture, so they might prefer to work out in privacy, at home — but they don’t know how. One person I encountered posted online to crowdsource advice on home equipment and routines. They said they didn’t want to go to a gym, but “I know I’m out of shape,” the poster confessed to their fellow Redditors.

The thread flooded with advice from simple workout routines to try to role models they could follow on social media. The advice included some very approachable strategies — something as simple as sitting in a chair with your legs outstretched and using your abdominal muscles to lift them from side to side over a water bottle. Some commenters recommended incorporating a resistance band and a workout ball. Health care providers have developed general recommendations for patients taking a GLP-1 drug: Mass General, for example, advises a mixture of 150 minutes a week of moderate exercise — activities like walking or riding a bike — or about 75 minutes of vigorous aerobic exercise like jogging or swimming laps in addition to two days of weight training and a steady dose of stretching and flexibility workouts.

While I found plenty of people concerned with unexpected muscle loss, there were also examples of patients proudly showing off their lean and muscular new physiques. It can be done.

But in this vision, GLP-1s are a jumpstart, not a shortcut. “Losing weight is everybody’s goal. Using a drug to jumpstart is an excellent way to do the process,” Patel said. “But if you’re not taking the first two steps, you’ll stumble until you fall flat on your face.”