Semaglutide and GLP-1 Weight-Loss Drugs: How They Work and What Side Effects Are Known

Drugs built around semaglutide — sold under brand names including Ozempic, Wegovy and Rybelsus — belong to a class called GLP-1 receptor agonists. Originally developed to treat type 2 diabetes, several of these medicines are now approved specifically for weight management, and their popularity has driven sustained public interest in how they work and what risks they carry.

How GLP-1 drugs work

According to the Cleveland Clinic, GLP-1 agonists mimic a naturally occurring gut hormone called glucagon-like peptide-1. They bind to GLP-1 receptors to stimulate insulin release from the pancreas, suppress the release of glucagon, slow stomach emptying and increase feelings of fullness. The combined effect is lower blood sugar and reduced appetite, which is why the same drug class is used both for diabetes and for weight loss.

The Cleveland Clinic lists several other medicines in the same class, including dulaglutide (Trulicity), liraglutide (Victoza) and exenatide, sold as Byetta or, in extended-release form, Bydureon. Tirzepatide, marketed as Mounjaro, works on a related but broader mechanism, acting on both GLP-1 and GIP receptors.

Established side effects

The most commonly reported side effects of GLP-1 agonists are gastrointestinal, the Cleveland Clinic states: loss of appetite, nausea, vomiting and diarrhea, especially when a patient starts treatment or increases the dose. The clinic also lists rare but serious adverse effects, including pancreatitis, medullary thyroid cancer, acute kidney injury and a worsening of diabetic retinopathy.

• Nausea, vomiting, diarrhea and loss of appetite — most common, especially early in treatment
• Pancreatitis — rare but serious
• Medullary thyroid cancer — rare, listed among serious risks
• Acute kidney injury — rare
• Worsening of diabetic retinopathy — rare, noted in patients with existing diabetic eye disease

New findings on hair and nails

A multinational case-control study presented at the European Academy of Dermatology and Venereology (EADV) Congress 2026 in Vienna examined hair and nail problems in people taking GLP-1 drugs. Researchers compared 575 GLP-1 users with 1,329 people who had type 2 diabetes or obesity but had never used the medications, recruiting participants in France, the United States, Brazil and Mexico, according to a press release distributed via EurekAlert and reporting by the German outlets Pharmazeutische Zeitung and t-online.

Nail detachment, known medically as onycholysis, was reported by 39% of GLP-1 users compared with 9% of controls — more than four times as common. Nail discoloration affected 46% of users versus 17% of controls, and 66% of users reported at least one nail problem overall, against 53% of controls.

Unusual hair loss was reported by 50% of GLP-1 users compared with 34% of controls. Loss of hair volume or density affected 42% of users versus 19% of controls, and hair loss that began only after starting treatment was reported by 26% of users against 12% of controls. Scalp redness was roughly three times more frequent among users, per the same sources.

What researchers say about causation

The study's authors, dermatologists Charles Taïeb and Bruno Halioua, stressed that the design — a cross-sectional comparison relying on patient-reported symptoms — cannot establish that GLP-1 drugs caused the nail or hair changes, according to the EurekAlert release and t-online's reporting. About half of the GLP-1 users in the study said they had experienced nail problems even before starting treatment, and the differences between groups remained significant even among participants who had lost similar amounts of weight, suggesting weight loss alone does not explain the pattern.

Researchers also noted that when hair loss occurred, it was rarely an isolated symptom — it tended to appear alongside scalp symptoms such as itching, redness or scaling, which led them to hypothesize that inflammatory processes on the scalp, rather than simple hormonal hair shedding, might be involved, according to t-online's summary of the findings. The study was conducted with institutional support from Ducray Laboratories, part of the Pierre Fabre Group, per the EurekAlert release.

Dermatologist Bruno Halioua was quoted by Pharmazeutische Zeitung as saying the changes observed are usually benign and do not, on their own, justify stopping an effective weight-loss or diabetes treatment.