BMJ review links the biggest fat loss among obesity drugs to the biggest lean mass loss

A network meta-analysis published July 8, 2026 in The BMJ pooled 262 randomized trials covering 99,791 people and 19 obesity drugs. Its central finding is a trade-off: tirzepatide produced the largest drop in fat mass, 25.7%, and also the largest drop in lean mass, 8.3%, more than any other drug on either measure. No drug improved quality of life by a margin researchers consider meaningful ^[1].

The trials lasted 12 to 172 weeks and tested drugs against lifestyle modification alone, placebo, or one another. Searches of Medline, Embase and the Cochrane Library closed on November 12, 2025 ^[1].

At one year, the analysis found moderate to high certainty evidence that several drugs beat lifestyle change alone on weight. Tirzepatide (sold as Mounjaro and Zepbound) led at a mean difference of 14.9% (95% confidence interval 16.0% to 13.9%), followed closely by the combination cagrilintide-semaglutide, or CagriSema, at 14.8%. Oral semaglutide came in at 10.9%, orforglipron at 9.9%, injectable semaglutide at 9.8%, and phentermine-topiramate at 8.1% ^[1].

Three drugs not yet on the US market, ecnoglutide, mazdutide and retatrutide, showed reductions between 13.1% and 14.6%, but that evidence was graded very low to low certainty ^[1].

Side effects grew along with the weight loss. The drugs most often stopped because of adverse events were orforglipron, naltrexone-bupropion, liraglutide, phentermine-topiramate, CagriSema and oral semaglutide, with risk ratios from 1.9 to 4.2. Gastrointestinal problems climbed most with naltrexone-bupropion, oral semaglutide, orforglipron and tirzepatide, at risk ratios of 3.1 to 4.2. Fatigue was highest for naltrexone-bupropion (risk ratio 8.9, an extra 331 cases per 1,000 people over a year), orforglipron (3.4; 100 more per 1,000) and CagriSema (3.2; 92 more per 1,000) ^[1].

Only injectable semaglutide was tied to fewer deaths from any cause (risk ratio 0.81, 0.72 to 0.93) and fewer heart attacks (0.72, 0.61 to 0.85). The authors caution that those estimates draw heavily on cardiovascular outcome trials run in people already at high heart risk. Injectable semaglutide (0.43, 0.21 to 0.84) and tirzepatide (0.49, 0.27 to 0.88) were both linked to lower heart failure risk. Kidney failure was not convincingly reduced by any drug ^[1].

Quality-of-life data came from 43 trials with 45,663 participants. Every drug's mean difference stayed under 5 points on the scales used, against a 10-point threshold the researchers treat as the smallest change a patient would notice ^[1].

Why it matters for patients

The phrase "obesity drug" turns out to say little about what a person gets. The largest fat-mass reductions arrived attached to the largest lean-mass reductions, and the review did not report whether that lean loss led to weakness, falls or other functional problems over time ^[1].

The mortality and heart-attack signal belongs to one drug in one form, injectable semaglutide, and rests mostly on trials of people who already had cardiovascular disease. Whether the same protection extends to lower-risk patients has not been established ^[1].

Dose and patient characteristics made no credible difference to how well the drugs worked, with one exception: longer trials of injectable semaglutide showed larger weight reductions ^[1].

What happens next

CagriSema and mazdutide are under regulatory consideration, the paper notes, without giving dates ^[1]. Because the literature search stopped in November 2025, trials reported afterward fall outside the analysis ^[1]. The review is registered with PROSPERO as CRD42024507993 and is accompanied by a linked editorial in The BMJ ^[1].