As millions flock to GLP-1s, doctors warn the drugs can cause rapid and significant muscle loss.
5 min
Chanel Robinson achieved exactly what the gold rush of blockbuster weight-loss drugs promised: She lost nearly 100 pounds, lowered her cholesterol to normal levels and reined in her polycystic ovary syndrome.
Yet, nearly three years into her journey on Mounjaro, the 30-year-old from Atlanta, Ga., is discovering the hidden costs of the slimmed-down life.
Robinson experiences muscle fatigue daily, feeling physically weak, frail and often cold. Robinson said she experiences bursts of sluggishness sporadically during the day, and has trouble with basic tasks like opening a jar. “It shouldn’t be this difficult,” she said.
GLP-1 drugs like Ozempic, Mounjaro and Zepbound have been a success for public health and the pharmaceutical companies that make them. Obesity rates are falling, the volume of food consumed in America is declining and retailers report a slump in sales of plus-size apparel. It has improved health and happiness for millions of people.
But for at least some of the 13 million Americans taking them, losing muscle along with fat is an unexpected downside that isn’t broadly discussed or immediately apparent.
The drugs can cause rapid and significant loss of lean muscle mass, up to 10%, comparable to a decade or more of aging, according to an analysis published by the American Diabetes Association.
The loss of lean tissue is similar to weight loss from dieting, but the magnitude over a short period can lead to frailty, instability and lack of coordination, doctors and researchers say. Another concern is that losing muscle could slow down patients’ metabolism, leading to weight regain.
“We are curing obesity by encouraging frailty,” said Daniel Green, principal research fellow at the University of Western Australia, who contributed to the analysis. Many taking weight-loss medications initially lose fat and feel great, but quickly start to feel weak and lethargic, he said.
Green’s research showed that the rate of muscle loss could be slowed significantly by regular strength workouts. “It should say ‘must be taken with resistance training’ on the box,” he said.
Drugmakers say weight-loss drugs should be taken only on the advice of a physician and as part of a long-term plan that includes diet and exercise.
A spokesperson for Eli Lilly, maker of Zepbound, said Food and Drug Administration guidelines say it should be used “with increased physical activity.” The spokesperson added: “Sustainable weight loss is about more than a number on a scale.”
Both Eli Lilly and Novo Nordisk said clinical trials showed users did lose some lean muscle tissue, though at far lower rates than fat. Liz Skrbkova, a spokeswoman for Novo Nordisk, said that trials for its drug Wegovy showed changes in muscle mass didn’t “significantly differ” from patients who took a placebo. Eli Lilly said users lost three times more fat weight than lean tissue.
Rayna Kingston, 30, from Denver, said her injections of Zepbound left her feeling so tired the following day that she struggled to complete anything other than basic tasks. She said she shifted her dose to a Sunday because Mondays were her least busy day. Her partner would bring her meals in bed because she felt so weak.
She stopped exercising, and said her doctor didn’t give her any guidance on strength training or muscle maintenance. “I was relying on Reddit forums to understand what was happening to my body,” she said. She got so frustrated with the fatigue she came off the medication just under two months later.
Experts say that losing muscle at such a rate can be especially dangerous for those over 50 or with osteoporosis or limited mobility as it could lead to an increased risk of injury. “Loss of muscle mass is detrimental to moving around and quality of life, but it is also not safe,” said Katsu Funai, associate professor at the University of Utah.
Elderly Americans are set to be able to get GLP-1s from Medicare from July.
There is also pushback from doctors and regulators against using weight-loss drugs as a “quick fix” to lose a bit of weight.
People who take GLP-1s regain weight four times faster than those who lose weight through lifestyle interventions, and weight regained is often mostly fat, according to a recent analysis published in the British Medical Journal. There currently are few, if any, guidelines or studies on de-prescribing the drugs, researchers say.
The nurse practitioner who prescribed Robinson the medication didn’t warn her that resistance training is essential to maintaining muscle mass, Robinson said. She said she regrets not exercising and now does Pilates once a week.
In the haste to disrupt the obesity epidemic, weight loss has been treated as the singular, undisputed metric of success, which experts say is problematic.
“People worship body weight as an outcome measure because it’s simple, quick and inexpensive,” said Green. “But what matters is fat and muscle mass, which is more expensive to measure as it requires an MRI.”
Grace Parkin, 34, a property manager from Sheffield, England, has lost 125 pounds after she started taking Mounjaro in 2024. “I don’t care about my muscle mass as long as I’m a healthy weight,” she said.
The doctor who prescribed the drug didn’t tell her to exercise, though the pharmacy that sold the medication gave her information on exercise and protein intake, she said.
She didn’t exercise and said she soon felt side effects: a “deathly cold, from the inside” likely because of the drug. Still, she vowed to keep going, saying the weight loss was worth it.
In response to some of the side effects, drug companies are hoping to develop weight-loss treatments aimed at preserving or even building lean muscle mass.
German drugmaker Boehringer Ingelheim recently said it had promising results from one such drug. Eli Lilly last September halted a trial of a similar drug.
While weight-loss medications are designed as lifelong treatments for chronic diseases, namely obesity and Type 2 diabetes, they are increasingly marketed as lifestyle fixes.
Tennis superstar Serena Williams, who used GLP-1s to slim down after having children, was featured in this year’s Super Bowl commercial promoting telehealth company Ro’s weight-loss medication.
Serena Williams poses for an ad campaign for a weight-loss drug. Ro/Handout/Reuters
Women may be particularly vulnerable to the drugs’s side effects, which can also include nausea, diarrhea, migraines and rarer cases of pancreatitis.
A study last year from a university hospital in Turin, Italy, showed that women are more prone to adverse reactions to weight-loss drugs than men, including muscle loss.
Green, the researcher, said the issue is of particular concern to those taking GLP-1s recreationally and who don’t have much muscle mass to begin with. Others say a lack of oversight is compounding the issue.
“Patients are self-reporting, and telehealth companies don’t have the patient in front of them to conduct a proper medical assessment,” said Rupal Mathur, an internist in Houston whose practice specializes in weight loss.
She said medical spas are prescribing off-label drugs that don’t meet the criteria set out by the FDA that justify a prescription.
The number of people taking weight-loss drugs who are not living with obesity or Type 2 diabetes is difficult to track since it is unregulated.
However, an analysis by the FDA from 2023 found that more than half of new Ozempic and Mounjaro users didn’t have Type 2 diabetes.
Scientists are calling for more clinical trials to pin down the full effects of weight-loss drugs on muscle loss in different demographics.
“The only studies that have been done have looked at people living with obesity or Type 2 diabetes,” said Green. “That makes it all the more concerning for those using weight-loss drugs in an ad hoc or unregistered way.”
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AI doesn’t rebel—people design, deploy and profit from it. The real danger lies in allowing tech companies to escape accountability while shaping regulations that protect their dominance.
4 min
A wave of corporate warnings and technical disclosures has flooded the media, with headlines worrying over “swarms” of rogue artificial-intelligence agents launching “unprecedented” cyberattacks, outsmarting their makers, and inching toward a terrifying autonomy. The most revealing part of this narrative isn’t what the software did. It’s who is telling the story—and why. When corporate leaders publicly insist that the systems they financed, engineered and deployed are suddenly beyond their power to contain, skepticism isn’t only healthy; it is essential.
For years, Silicon Valley has drawn scrutiny from civil society and global regulators over tangible harms such as youth mental health deterioration and systematic privacy violations. Today, industry figures seem to be trying to change that public image. Loudly blowing the whistle on their own systems—just as two of the leading companies were preparing for massive initial public offerings—lets AI executives position themselves as a new generation of leaders who have come to terms with their societal responsibilities. They seem to want us to believe that they no longer want to “move fast and break things” but will instead stand as vigilant guardians between humanity and a technological apocalypse.
There is one glaring problem: Software doesn’t rebel. A mathematical model possesses neither intent, malice nor the will to defy its creators, let alone extinguish our species. AI is a human artifact, engineered for profit.
When an agentic model in an evaluation sandbox connects to an unauthorized server or executes an exploit, it hasn’t staged a coup. It has tried to meet the human-defined objectives set out before it through a path its designers failed to constrain. It’s the digital equivalent of the King Midas myth, in which the king’s ill-defined wish turns even his food and drink into gold.
That powerful experimental models were able to discover novel vulnerabilities and breach external systems isn’t a sign of a dangerous superintelligence but of human error or negligence. There is no sentient actor lurking in the weights to be reasoned with, feared or pacified. There are only human software engineers, product managers and corporate boards deciding which guardrails are worth the latency cost and which permissions can be skipped in the race to market.
Policymakers and voters need to resist AI exceptionalism. In any other discipline—from civil engineering to pharmaceuticals—courts and regulators treat a system failure as evidence of bad product design and inadequate safety testing. If an aircraft crashes, we focus on finding the engineering defect, correcting it, and enforcing established liability standards for the damage created.
By leaning on an anthropomorphic narrative, Silicon Valley attempts to repackage its specific human choices that led to experimental, powerful models behaving unexpectedly during tests as an existential peril. Elevating the issue to a cosmic scale leaves the public paralyzed and takes ordinary product accountability off the table.
In the cutthroat race for venture capital and market dominance, building guardrails slows down deployment. Grandstanding about uncontrollable power costs nothing and generates billions of dollars in free publicity, justifying stock prices, all while cultivating an aura of technological capability not only to build the frontier but also ultimately to rein it in.
Governments need to recognize regulatory capture when it stares them in the face. Tech leaders’ strategy looks transparent: Alarm Washington and Brussels into creating a regime in which only trillion-dollar incumbents with fully staffed compliance and safety departments can legally operate. By sitting at the policymakers’ tables before anyone else, these companies can help draft rules digging an impassable moat protecting them from open-source developers and upstart competitors, domestic or international. The real danger is in further concentrating the tech industry into the hands of only a few companies with deep pockets.
Beijing and Washington have brushed off those tech leaders’ calls, albeit for very different reasons. Chinese state media dismissed them as part of the “Cold War playbook” and intended to preserve U.S. dominance. Xi Jinping argued for exactly the opposite at the Brics Summit on Sept. 12, calling on Brics countries to “strengthen cooperation in the field of AI, encourage open source, openness, collaboration and sharing, and break new grounds and scale new heights.” President Trump, steeped in a doctrine of unfettered capitalism and technological supremacy, called fears that AI could destroy humanity a “hoax.” Vice President JD Vance warned that AI companies “begging the government to regulate them” looked like a “Trojan Horse.”
Striving to pursue its “European way” on AI and assert regulatory leadership, Europe, by contrast, welcomed the call. European Union President Ursula von der Leyen made this clear at the State of the EU speech last Wednesday and announced that the EU will invite “the main frontier labs for a discussion on how we can support ongoing industry efforts to pace the frontier.”
Europe has been here before. In an effort to lead global regulation and react to fears borne from ChatGPT, Europe rushed its landmark AI Act into law in 2024. Already the world’s most restrictive rulebook, the framework quickly proved too broad and complex to enforce. Stalled by implementation delays and concerns about European competitiveness, the EU postponed the law’s full rollout, leaving regulations uncertain.
AI should be regulated—risks exist and should be taken seriously. But governments need to act based on available evidence and verified facts, not corporate PR panic, the views of industry insiders, or the desire for quick political wins. The greatest danger facing society isn’t that software will awaken and overthrow its human masters. It is that we will allow the creators of the software to abdicate human responsibility for the systems they choose to build and help them pull up the ladder to market access behind them.
