Widely used GLP-1 drugs, including Ozempic and Mounjaro, may carry an unexpected downside: a small but measurable increase in hair loss.
A large study of adults with type 2 diabetes found that people taking the medications were more likely to develop alopecia than those using two other classes of diabetes drugs.
The findings, published in The BMJ, do not prove that GLP-1 receptor agonists directly cause hair loss. However, they provide some of the strongest evidence so far that the association deserves greater attention as drugs such as semaglutide and tirzepatide become increasingly common.
Researchers stressed that the absolute risk was low. Even so, information about a potential effect on hair could matter to patients when they weigh the benefits and drawbacks of treatment with their clinicians.
Evidence Behind the Hair Loss Link
Alopecia has previously appeared in individual reports and safety monitoring data involving GLP-1 receptor agonists, particularly semaglutide and tirzepatide. Until now, however, researchers have had limited evidence showing how the risk compares with that of other diabetes medications.
To investigate, the team analyzed electronic health records from the University of Pennsylvania Health System (Penn Medicine). The study included adults with type 2 diabetes who began treatment with a GLP-1 receptor agonist, an SGLT-2 inhibitor, or a DPP-4 inhibitor between January 2019 and September 2024.
One analysis compared 12,004 GLP-1 users with 15,221 people taking SGLT-2 inhibitors. A second included 11,964 GLP-1 users and 11,233 people taking DPP-4 inhibitors.
How Researchers Compared Diabetes Drugs
The groups differed in several important ways. Compared with SGLT-2 inhibitor users, those taking GLP-1 drugs were younger (mean age 58 vs. 65), had a higher body mass index (36.2 vs. 32.3), and had lower rates of cardiovascular disease and chronic kidney disease.
Similar differences appeared in the second comparison. GLP-1 users were younger (mean age 58 vs. 67) and had a higher body mass index (36.2 vs. 31.3) than people taking DPP-4 inhibitors.
Researchers used statistical methods to account for age, sex, ethnicity, pre-existing conditions, body mass index, other medications, and additional factors that might influence hair loss.
GLP-1 Drugs Show Higher Alopecia Risk
After those adjustments, GLP-1 receptor agonists were associated with a 37% higher risk of alopecia than SGLT-2 inhibitors. The recorded rates were 6.91 versus 5.04 cases per 1,000 person-years.
Compared with DPP-4 inhibitors, GLP-1 drugs were associated with a 68% increase in risk, with rates of 6.53 versus 3.89 cases per 1,000 person-years.
Further analysis suggested that the association involved non-scarring alopecia (where hair follicles remain intact, leaving the potential for regrowth). GLP-1 users had a 53% higher risk of this form of hair loss than SGLT-2 inhibitor users and a 72% higher risk than DPP-4 inhibitor users.
Why Rapid Weight Loss May Affect Hair
The study could not determine exactly why the difference occurred. One possibility is that the drugs affect hair indirectly through rapid weight loss rather than acting directly on hair follicles.
Significant weight loss can push more hairs than usual into a resting phase, leading to increased shedding several months later. This response is often temporary, but it can be distressing and may not be immediately recognized as connected to changes in weight or nutrition.
Rapid weight loss can also contribute to iron or zinc deficiencies, both of which may disrupt the normal hair growth cycle. Hormonal and metabolic changes could play a role as well, although the researchers said more work is needed to separate these possible mechanisms.
Important Limits of the Findings
Several limitations prevent firm conclusions. Because the researchers relied on health records, they could not consistently determine the severity, extent, duration, or reversibility of the hair loss after treatment stopped. Mild cases that were never reported to a clinician may also have been missed.
The researchers nevertheless noted that the study used high-quality data from a large and representative patient population. The findings also remained consistent across additional analyses, supporting the reliability of the observed association.
“Our findings extend previous anecdotal safety signals and provide more systematic evidence to inform clinical awareness of this potential adverse effect,” they concluded.
Reference: “Risk of hair loss associated with glucagon-like peptide-1 receptor agonists in adults with type 2 diabetes: target trial emulation” by Huilin Tang, Bingyu Zhang, Yiwen Lu, Dazheng Zhang, Ruishan Liu, Yuan Lu, George Cotsarelis, David A Asch and Yong Chen, 22 July 2026, BMJ.
DOI: 10.1136/bmj-2026-100077
This study was supported by the NIH/National Institutes of Health.
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