GLP-1 Weight Loss Drugs Work Better in Women Than Men, Meta-Analysis Finds
GLP-1 receptor agonists - the class of drugs that includes semaglutide and tirzepatide - have become among the most widely prescribed medications in the United States. Their weight loss effects are substantial by the standards of pharmacological interventions, averaging 10 to 20 percent of body weight in clinical trials depending on the specific drug and dose. But averages obscure variation, and clinicians and patients alike want to know: who benefits most?
A systematic review and meta-analysis published in JAMA Internal Medicine examined treatment effect heterogeneity across major subgroups, analyzing data on GLP-1 receptor agonist use for weight loss in adults. The headline finding is that women lose more weight on these drugs than men. Across other key subpopulations - age groups, racial and ethnic categories, baseline body mass index categories - the efficacy of GLP-1 drugs was broadly consistent.
The Sex Difference in Weight Loss Response
The analysis, led by G. Caleb Alexander of Johns Hopkins, found that women in clinical trials of GLP-1 receptor agonists lost significantly more weight than men on the same drugs at the same doses. The magnitude of the difference varied across individual trials, but the pattern was consistent enough to show up clearly in the pooled analysis.
The biological reasons for this difference are not fully established. Sex-based differences in body composition, hormonal environments, gut motility, and the distribution of GLP-1 receptors in various tissues have all been proposed as potential contributors. Women typically have higher baseline percentages of body fat relative to body weight than men, and some evidence suggests that GLP-1 drugs may act differently on adipose tissue compared with lean tissue. Whether the sex difference in response reflects pharmacodynamics, pharmacokinetics, or behavioral and social factors that differ by sex is a question the meta-analysis cannot resolve.
Consistency Across Other Subgroups
The finding of consistent efficacy across age groups, racial and ethnic populations, and BMI categories is reassuring for clinicians treating diverse patients. Concerns that GLP-1 drugs might work substantially better in younger patients, or in specific racial groups with different metabolic profiles, are not borne out by the aggregated data. Patients at lower baseline BMI showed similar relative weight loss to those with higher starting weights, addressing a question relevant to prescribing decisions as the drugs are increasingly considered for patients who are overweight but not severely obese.
What This Means for Prescribing Decisions
The sex difference in treatment effect is unlikely to change prescribing patterns fundamentally - GLP-1 drugs are effective in both men and women, even if women show larger average losses. But the finding does have implications for setting realistic expectations when starting treatment. A male patient who loses 10 percent of his body weight on a GLP-1 drug has achieved a clinically meaningful outcome, even if a female patient at the same dose might lose 12 or 14 percent.
The meta-analysis draws on clinical trial data and inherits the limitations of those trials. Clinical trials typically enroll healthier participants than the general population, and real-world effectiveness may differ from trial results. The analysis also cannot speak to how these drugs perform over extended periods beyond the duration of the included trials.