Six things this study found that nobody else is telling you

1. Only one drug has real evidence of saving lives

Injectable semaglutide, the active ingredient in Wegovy, was the only drug in the whole study with solid evidence of reducing deaths from any cause, a 19 percent relative reduction, and heart attacks, a 28 percent relative reduction. It also cut the risk of heart failure by more than half. Tirzepatide showed a similar reduction in heart failure risk too, though the evidence for cutting heart attacks specifically wasn’t as strong.

None of the other drugs, including Mounjaro at its top dose, currently have this level of evidence behind them for actually extending life or protecting the heart. That doesn’t mean they don’t, it means the trials proving it haven’t been done yet, largely because semaglutide has simply been studied for longer and in larger cardiovascular outcome trials. If reducing your risk of a heart attack or dying early is your main priority rather than the number on the scale, this is the single most important finding on this page.

2. Despite the weight loss, nobody’s quality of life meaningfully improved

This is genuinely surprising. Researchers measured quality of life using a standard 100-point wellbeing scale, where a 10-point shift is considered the smallest change a person would actually notice in daily life. Every single drug studied, including Mounjaro, both forms of Wegovy, and CagriSema, fell short of that 10-point threshold. The best result, from phentermine-topiramate, was only 4.3 points.

In plain terms, people are losing significant weight, in some cases three or four stone, and researchers still aren’t seeing it translate into a clear, measurable improvement in how people say they feel day to day. That doesn’t mean individuals don’t feel better, plenty do, but as a group, across dozens of trials, the effect isn’t showing up strongly in the data yet. It’s a reminder that weight loss and wellbeing aren’t automatically the same thing.

3. The weight comes back faster than most people expect

The BMJ authors pulled together separate data from 37 studies specifically looking at what happens after people stop treatment. On average, people regained weight at a rate of about 0.4kg a month, and were projected to be back to roughly their starting weight within about 1.7 years, alongside losing the blood pressure and blood sugar improvements they’d gained too.

Separately, real-world data cited in the same paper suggests roughly half of patients stop taking these drugs within the first year anyway, for all sorts of reasons, cost, side effects, or simply life getting in the way. Put those two facts together and the honest picture is this. Unless you’re planning to stay on the medication long term, or use the time on it to build lasting changes to how you eat and move, the weight loss is unlikely to be permanent on its own.

4. Muscle loss varies a lot more between drugs than people realise

Mounjaro lost the most fat of any drug studied, but it also caused the most muscle loss, an average 8.3 percent reduction in lean mass. Injectable Wegovy also caused a meaningful drop, around 5.8 percent. The Wegovy tablet, by contrast, showed little to no measurable effect on muscle mass in the trials reviewed, a genuinely useful and under-reported difference if preserving strength matters to you, particularly for older adults.
This is exactly why every major guideline, including this study’s authors, recommends combining any of these drugs with resistance exercise, lifting weights or bodyweight training, not just walking or cardio, to protect muscle while the fat comes off.

5. Retatrutide isn’t approved yet, but the early signal is real

Retatrutide is the drug more people are asking us about than almost anything else on this site, and it’s worth being upfront about where it sits in this analysis. The BMJ researchers grouped it alongside two other emerging drugs, mazdutide and ecnoglutide, none of which are approved in the UK yet, and estimated weight loss in the region of 13.1 to 14.6 percent. That would put it roughly on par with Mounjaro and CagriSema, potentially higher once the full trial data matures.

The important caveat is the certainty rating attached to that number is very low to low, the lowest confidence grading in the entire study. That’s not a comment on the drug itself, it simply reflects that retatrutide has been studied in far fewer, smaller trials than the established options so far, which is exactly what you’d expect for something still working through the approval pipeline rather than a red flag about the drug.

What we can say with more confidence, because it comes from retatrutide’s own dedicated Phase 3 trial rather than this pooled estimate, is that the TRIUMPH-1 results published in May 2026 showed 28.3 percent average weight loss at the highest dose, a genuinely striking figure. We track the approval timeline, trial results and UK availability in detail on our dedicated Retatrutide UK guide, updated as soon as anything changes, worth bookmarking if you want to be ahead of the story when it lands here.

6. What about Saxenda, orlistat and the older options?

Worth an honest mention, since they’re still widely available and prescribed. Liraglutide, sold as Saxenda, and orlistat, the only weight loss drug available over the counter in the UK, were both included in this analysis. Neither showed a convincing difference from lifestyle changes alone for weight loss, once pooled across all the available trial data. The same was true for naltrexone-bupropion, exenatide and dulaglutide.

That doesn’t necessarily mean these drugs don’t work for anyone, individual results vary, and orlistat works through a completely different mechanism, reducing fat absorption in the gut rather than suppressing appetite. But if you’re choosing a treatment based purely on the strength of the evidence, this study is a useful, honest reality check on where the older generation of options currently stands next to the newer GLP-1 and dual-agonist drugs.