GLP-1 Weight-Loss Drugs Tied to Younger Biological Age, but Side Effects Still Being Mapped

GLP-1 agonist drugs work by repressing hunger. They have been approved for treating diabetes, chronic kidney disease and obesity, and they can also be prescribed for some people who are overweight or at risk of certain cardiovascular diseases. Research has suggested they might also help people with substance-use disorders, and they have been investigated for potential benefits in neurodegenerative disease and cancer. A recent Gallup poll found 11% of Americans are taking a GLP-1 drug for weight loss, up from 3% in 2024, and 15% say they have used one for weight loss at some point.

Like any drug, GLP-1s can come with side effects, and researchers are still determining which ones are caused by the drugs and how common they are. The most common side effects are gastrointestinal: nausea, vomiting, diarrhea and constipation. The drugs have also been linked to pancreatitis and gallstone disease. Some claim that in rare cases the drugs might cause damage to nerves behind the eye. Dozens of people are suing Novo and Eli Lilly after developing a condition that can lead to sudden vision loss, claiming their symptoms were brought on by the companies' GLP-1 drugs. Both companies dispute the claims, and research into the link is mixed.

Effects on hair and nails are also being studied. When Savanna Vidal at the George Washington University School of Medicine and Health Sciences in Washington, DC, and colleagues assessed electronic health data from 67 US health-care organizations, they found GLP-1 use was associated with an increased risk of hair loss. It is still not thought to be common. At a conference in Austria last week, another group presented results of a smaller study suggesting that 66% of GLP-1 users reported at least one nail disorder, in some cases involving nail detachment. Nail conditions were also fairly common among people who did not take the drugs, and the authors do not claim the drugs are causing nails to fall out.

Side effects might look different in children, but there is not much data at the moment. Pediatric side effects will be something to watch given that, 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. Child prescriptions are still rare, but they have been rising.

On Wednesday, the World Health Organization released its first guidelines on managing obesity in children and adolescents. The WHO estimates that 70 million children aged five to nine were living with obesity in 2024. The organization explicitly says it does not recommend pharmacological treatment for kids under 10. “This recommendation accounts for the lack of evidence on both benefits and the potential adverse events and consequences of the different medications and/or their active ingredients on normal growth, development, physiological parameters, and mental health,” the guidelines state.

MIT Technology Review reported that there has been a large amount of research into these drugs, with hundreds of other studies likely under way, and that more evidence will emerge as the science evolves.