BMJ Study Links GLP-1 Receptor Agonists to Higher Hair Loss Risk in Type 2 Diabetes

The BMJ published a study on July 22, 2026 finding that adults with type 2 diabetes who started taking a GLP-1 receptor agonist had a higher relative risk of clinically recorded hair loss than those who started two other classes of diabetes medication. The study, led by researchers at the University of Pennsylvania's Center for Health AI and Synthesis of Evidence, used a target trial emulation design applied to electronic health records from the University of Pennsylvania Health System, known as Penn Medicine. The paper notes that alopecia has previously been reported as a possible side effect of GLP-1 receptor agonists, particularly semaglutide and tirzepatide, but says studies directly comparing alopecia risk against other diabetes drug classes have been lacking.

Researchers identified adults with type 2 diabetes who newly started a GLP-1 receptor agonist, an SGLT-2 inhibitor, or a DPP-4 inhibitor between January 2019 and September 2024. In one comparison, 12,004 patients who started a GLP-1 receptor agonist were compared with 15,221 patients who started an SGLT-2 inhibitor. In a second comparison, 11,964 GLP-1 receptor agonist initiators were compared with 11,233 DPP-4 inhibitor initiators. At baseline, GLP-1 receptor agonist users were younger and had a higher body mass index than users of either comparator drug: mean age 58 versus 65 and mean BMI 36.2 versus 32.3 compared with the SGLT-2 inhibitor group, and mean age 58 versus 67 and mean BMI 36.2 versus 31.3 compared with the DPP-4 inhibitor group. The study used inverse probability of treatment weighting and Cox proportional hazards models to adjust for age, sex, ethnicity, pre-existing conditions, other medication use, and body mass index, along with sensitivity analyses including negative control outcome calibration.

After adjustment, GLP-1 receptor agonist use was associated with a 37 percent higher risk of alopecia than SGLT-2 inhibitor use, corresponding to an incidence of 6.91 cases per 1,000 person-years among GLP-1 receptor agonist users versus 5.04 among SGLT-2 inhibitor users (hazard ratio 1.37, 95% confidence interval 1.08 to 1.73). Compared with DPP-4 inhibitor use, GLP-1 receptor agonist use was associated with a 68 percent higher risk, corresponding to 6.53 cases per 1,000 person-years versus 3.89 (hazard ratio 1.68, 95% confidence interval 1.28 to 2.20). Subtype analyses found the association was specific to non-scarring alopecia, a form in which hair follicles remain intact and regrowth remains possible, with hazard ratios of 1.53 (1.18 to 1.97) versus SGLT-2 inhibitors and 1.72 (1.28 to 2.31) versus DPP-4 inhibitors.

The study authors proposed that rapid weight loss, a well-established trigger of temporary hair shedding, could help explain the association, along with possible nutrient deficiencies such as low iron or zinc that can accompany significant weight loss and disrupt the hair growth cycle. They said hormonal changes might also play a role but that further studies are needed to clarify the underlying mechanisms. The authors acknowledged limitations: the electronic health record data did not capture the severity, extent, duration, or reversibility of hair loss after stopping treatment, and residual confounding from unmeasured factors could not be ruled out. "Our findings extend previous anecdotal safety signals and provide more systematic evidence to inform clinical awareness of this potential adverse effect," the authors concluded, according to a BMJ Group press release accompanying the paper.

Dr. Marie Spreckley, a postdoctoral researcher in epidemiology at the University of Cambridge who was not involved in the study, said in comments distributed by the UK Science Media Centre that the target trial emulation approach, active comparator groups, and multiple sensitivity analyses "strengthen confidence in the findings," but cautioned that, "as with all observational studies, it cannot establish causality, and the possibility of residual confounding remains." She added that the absolute risk difference was small: "In practical terms, this means around two to three additional clinically recorded cases of hair loss per 1,000 person-years of treatment compared with the alternative diabetes medications."

Semaglutide and tirzepatide are both approved by the U.S. Food and Drug Administration, semaglutide as Ozempic and Rybelsus for type 2 diabetes and as Wegovy for chronic weight management, and tirzepatide as Mounjaro for type 2 diabetes and Zepbound for chronic weight management. This study did not report results broken down by individual drug within the GLP-1 receptor agonist class, and it does not change the approved indications, prescribing information, or regulatory status of any GLP-1 receptor agonist. The findings describe an observational association identified in routine clinical data, not a confirmed causal effect, and this report does not constitute treatment or dosing guidance.