The Weight-Loss Drug Revolution Is Outrunning Its Own Science

The numbers alone tell a story of a drug class racing ahead of its evidence. According to MIT Technology Review's biotech newsletter The Checkup, a recent Gallup poll found that 11% of Americans are taking a GLP-1 drug for weight loss, up from 3% in 2024 — and 15% of Americans say they have used one at some point. The drugs, which suppress appetite, are approved for diabetes, chronic kidney disease, and obesity, and are also prescribed to some people who are overweight or at risk of certain cardiovascular diseases.

That pace of adoption means the real-world experiment is happening in public, and the side-effect map is still being drawn.

Benefits beyond the scale

Researchers have spent years documenting what these drugs might do beyond shedding pounds. According to the report, research presented at an aging meeting in Boston suggested that overweight and diabetic people taking GLP-1s have a biological age roughly two to three years younger than comparable people not on the drugs. People in the aging field have reportedly described GLP-1s as longevity drugs for some time — at least for those who are overweight or diabetic.

There is also research suggesting the drugs could help people with substance-use disorders, and they have been investigated for potential benefits in neurodegenerative disease and cancer, according to the newsletter.

The known — and the emerging

The most common side effects are gastrointestinal: nausea, vomiting, diarrhea, and constipation. The drugs have also been linked to pancreatitis and gallstone disease, the report notes.

Beyond those, the picture gets murkier. Dozens of people are suing Novo Nordisk and Eli Lilly after developing a condition that can cause sudden vision loss, claiming their symptoms were brought on by the GLP-1 drugs the companies manufacture; both companies dispute the claims, and research into the link is mixed, according to the report.

Other effects are only now surfacing. When researchers at the George Washington University School of Medicine and Health Sciences examined electronic health data from 67 US health-care organizations, they found that GLP-1 use was associated with an increased risk of hair loss — though it is not thought to be common. And at a conference in Austria last week, another group presented results from a smaller study suggesting that 66% of GLP-1 users reported at least one nail disorder, in some cases involving nail detachment. Nail problems were also fairly common among people not taking the drugs, and the authors did not claim the drugs were causing the conditions, according to the report.

The pediatric question

The largest evidence gap may be in children. Between 2019 and 2026, there was a 310-fold increase in GLP-1 prescriptions for eight- to 11-year-old children with obesity in the US, according to NYU Langone research cited by the newsletter. Child prescriptions remain rare, but they are rising — and there is little data on how side effects might differ in young patients.

On Wednesday, the World Health Organization released its first guidelines on managing obesity in children and adolescents. Despite estimating that 70 million children aged five to nine were living with obesity in 2024, the WHO explicitly says it does not recommend pharmacological treatment for kids under 10, citing the lack of evidence on both benefits and potential adverse events for growth, development, physiological parameters, and mental health, according to the guidelines.

With hundreds of GLP-1 studies reportedly underway, the evidence will keep evolving. For now, the drugs remain what they have always been: remarkably effective for many, and still not fully understood.

Written by the BidAsk Newsroom. Based on reporting from the sources below.