Weight-loss medicines have become some of the most talked-about treatments in recent years.
Drugs such as Wegovy, Mounjaro, and several newer medicines can help people lose a large amount of weight, giving hope to millions living with overweight and obesity.
Obesity increases the risk of type 2 diabetes, heart disease, stroke, sleep apnea, arthritis, and several cancers.
Losing weight can lower many of these risks, but doctors also want to know whether these medicines improve people’s daily lives, reduce serious illnesses, and remain safe over the long term. A new analysis published in The BMJ suggests that the answer is more complicated than many people may expect.
Researchers reviewed 262 randomized controlled trials involving almost 100,000 adults. The participants had an average age of 49 years, about two-thirds were women, and the average body mass index was 35, which falls within the obesity range.
The studies compared 19 currently available or experimental weight-loss medicines with lifestyle changes, placebo, or other drugs. Follow-up lasted from 12 to 172 weeks.
The researchers examined much more than body weight. They also looked at body fat, muscle mass, quality of life, heart and kidney outcomes, and side effects such as nausea, vomiting, diarrhea, gallbladder problems, and tiredness. They also assessed how reliable the evidence was using the internationally recognized GRADE system.
The largest average weight loss after one year was seen with tirzepatide at about 14.9% of body weight and CagriSema at 14.8%. Oral semaglutide, orforglipron, injectable semaglutide, and phentermine-topiramate also produced substantial weight loss.
Several experimental medicines showed promising results, but the evidence supporting them was still limited.
However, greater weight loss generally came with more side effects. People taking the most effective medicines were also more likely to stop treatment because of stomach or bowel problems, fatigue, or other unwanted effects.
Tirzepatide reduced body fat the most but also caused the greatest loss of lean body mass, including muscle. Preserving muscle is important because it supports strength, mobility, and healthy aging.
The review also found that improvements in quality of life were generally small and not large enough to be considered clinically meaningful. In addition, most benefits disappeared after treatment stopped because many people regained weight, highlighting that these medicines often need to be continued long term.
When the researchers examined heart health, only a few medicines showed clear benefits. Injectable semaglutide reduced the risk of death from any cause, heart attack, and heart failure. Tirzepatide also lowered the risk of heart failure. No medicine convincingly reduced kidney failure.
The authors emphasize that treatment decisions should not be based on weight loss alone. Doctors and patients should also consider side effects, long-term safety, costs, availability, treatment burden, and personal preferences.
This is one of the largest and most comprehensive comparisons of obesity medicines published to date. Because it combines hundreds of randomized trials, it provides valuable information for doctors and patients. However, most studies lasted only one to three years, making it difficult to judge long-term safety and whether benefits continue for decades.
Some newer medicines were also supported by limited evidence. Overall, the review suggests that modern obesity drugs can produce impressive weight loss, but larger weight loss does not automatically translate into better quality of life or broader health benefits. Future long-term studies will be essential.
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