The newest weight-loss drugs work, but the biggest results tend to arrive with the biggest downsides. A large systematic review and network meta-analysis in The BMJ compared 19 medications for adults with overweight or obesity, producing one of the clearest side-by-side pictures to date of what each drug delivers and what it costs in side effects.
Why this comparison matters. New obesity medications have arrived quickly, and head-to-head trials between them are scarce, leaving patients, clinicians, and payers guessing about how they truly stack up. A network meta-analysis fills that gap by combining direct and indirect evidence so drugs that were never tested against each other can still be ranked, and this analysis was explicitly designed to inform real-world decisions.
What the study did. Researchers pooled 262 randomized controlled trials covering 99,791 participants and 19 drugs, with follow-up ranging from 12 to 172 weeks. They assessed 24 outcomes, from weight and body composition to cardiovascular events and quality of life, and rated the certainty of each finding using the GRADE framework, along with the Cochrane Risk of Bias 2 tool. Trials had to run at least 12 weeks and compare a drug against lifestyle modification, placebo, or another drug.
How the drugs ranked on weight loss. Compared with lifestyle changes alone at one year, and with moderate-to-high certainty, the largest average reductions came from tirzepatide (-14.9%), cagrilintide-semaglutide, also called CagriSema (-14.8%), oral semaglutide (-10.9%), orforglipron (-9.9%), injectable (subcutaneous) semaglutide (-9.8%), and phentermine-topiramate (-8.1%). Several emerging agents, ecnoglutide, mazdutide, and retatrutide, may produce similar or larger reductions of roughly 13% to 15%, but on very low to low certainty evidence, meaning those numbers could shift as more data arrive.
The trade-off: more weight loss, more harm. Larger benefits generally came with more side effects. Discontinuation because of adverse events was highest with orforglipron, naltrexone-bupropion, liraglutide, phentermine-topiramate, CagriSema, and oral semaglutide (risk ratios from 1.9 to 4.2). Gastrointestinal problems were most increased with naltrexone-bupropion, oral semaglutide, orforglipron, and tirzepatide (risk ratios 3.1 to 4.2). Fatigue also rose, most sharply with naltrexone-bupropion (risk ratio 8.9, an absolute increase of 331 more cases per 1,000 people over a year), orforglipron, and CagriSema.
Not all weight loss is the same. Body composition differed by drug. Tirzepatide reduced fat mass the most, by about 25.7%, but it also cut lean (muscle) mass the most, by about 8.3%, a reminder that scale weight alone does not capture what is being lost.
The cardiovascular and survival picture. This is where the drugs separated most. Injectable semaglutide was the only medication associated with reduced all-cause mortality (risk ratio 0.81) and fewer heart attacks (0.72), estimates drawn largely from cardiovascular outcome trials in higher-risk patients. Both injectable semaglutide (0.43) and tirzepatide (0.49) were linked to lower heart-failure risk. By contrast, no drug convincingly reduced kidney failure, and across 43 trials with 45,663 participants, none meaningfully improved quality of life beyond established thresholds.
How to read this, and an important caveat. These are prescription medications, and this article is not medical advice. Weight loss percentages are averages; individual responses vary, and the certainty of evidence differs sharply between well-studied drugs and newer ones. The right choice, if any, depends on a person's health profile, risks, other conditions, and goals, and should be made with a qualified clinician.
Bottom line. Obesity drugs differ substantially: a handful deliver large weight loss, only injectable semaglutide clearly showed cardiovascular and survival benefits, most did not improve quality of life, and stronger effects usually brought more side effects and dropouts. The study's own conclusion is that decisions should weigh benefits against harms through shared decision-making, not assume that more weight loss is always better.