Two weight-loss medications produced the greatest reductions in body weight in a major new study, but they also drove the highest rates of patients quitting due to side effects.
The analysis, published on July 8, 2026, and reported by Healthline, examined nearly 100,000 participants across 262 clinical trials. Researchers compared 19 weight-loss drugs against lifestyle changes alone, a placebo, or other medications. The study used a method called network meta-analysis, which allows researchers to compare treatments even when they have not been tested directly against each other.
Tirzepatide and cagrilinitide-semaglutide stood out from the rest. Both led to roughly 15% reductions in body weight after one year. Other drugs including oral semaglutide, orforglipron, subcutaneous semaglutide, and phentermine-topiramate helped participants lose between 8% and 11% of their body weight.
Emerging treatments such as ecnoglutide, mazdutide, and retatrutide also showed promise, though the evidence for those newer drugs remains limited.
The study tracked 24 separate outcomes. Researchers looked at percentage of body weight lost, changes in waist circumference, shifts in fat and muscle mass, rates of gastrointestinal symptoms and fatigue, rates of patients stopping treatment because of adverse effects, and serious health outcomes including heart attacks and death. Trial duration, drug dosage, and patient characteristics were also examined.
The central finding about side effects adds a layer of complexity to the picture of these medications. Greater weight loss was consistently associated with more nausea, diarrhea, and fatigue, and those symptoms were frequent enough to cause patients to stop taking the drugs. That pattern means the most effective medications by one measure performed worse by another.
The researchers drew data from major medical databases including MEDLINE, EMBASE, and the Cochrane Library, with records collected through November 2025. Trials had to last at least 12 weeks and involve adults with overweight or obesity, with or without related conditions such as type 2 diabetes or heart disease.
The study was designed to help patients, physicians, and policymakers make more informed decisions about obesity treatment. Experts cited in the Healthline report said the findings point to the importance of looking beyond weight loss numbers alone and developing better strategies for managing side effects, which can determine whether a patient stays on a medication long enough to benefit from it.
The drugs reviewed can also reduce heart disease risk and improve conditions such as type 2 diabetes and sleep apnea, adding to the stakes of matching each patient with the right treatment. As the number of available obesity medications continues to grow, the study's authors said physicians face an increasingly complex task in balancing the benefits and risks for individual patients.
