Three new Cochrane reviews conclude that tirzepatide, semaglutide and liraglutide produce clinically meaningful weight loss in adults with obesity, while evidence on long‑term safety, broader outcomes and equitable access remains limited. The findings will inform forthcoming World Health Organization guidance on obesity treatment.
Cochrane’s new systematic reviews, requested by the World Health Organization, examine three GLP-1–based medicines used for weight management and find consistent weight loss versus placebo while people remain on treatment. GLP‑1 receptor agonists entered clinical use for type 2 diabetes in the mid‑2000s and, in that setting, have reduced major cardiovascular events and slowed kidney disease progression in high‑risk patients, according to large trials and meta‑analyses. (cochrane.org)
The reviews synthesize randomized trials of each drug:
- Tirzepatide: nine studies (8 versus placebo) involving 7,111 adults; the main placebo comparisons include 6,361 participants. Cochrane reports weight loss in the medium term (up to about 1.5 years) with signals of maintenance at roughly 3.5 years, though long‑term estimates rest largely on one study. (cochrane.org)
- Semaglutide: 18 studies with 27,949 participants, showing sustained weight loss while on therapy at 6–24 months and likely beyond two years, alongside higher rates of mostly gastrointestinal adverse events. (cochrane.org)
- Liraglutide: 24 studies with 9,937 participants, increasing the share of patients achieving at least 5% weight loss; effects on percentage weight change beyond two years are limited or uncertain. (cochrane.org)
Cochrane’s press materials summarize average weight change across trials as approximately 16% for tirzepatide (12–18 months), about 11% for semaglutide (24–68 weeks), and 4–5% for liraglutide. These pooled percentages derive from the Cochrane news release and ScienceDaily write‑up of the reviews, not from a single head‑to‑head trial. (cochrane.org)
Across the three reviews, there was little to no difference versus placebo in major cardiovascular events, mortality, or quality of life within the obesity-treatment trials, and gastrointestinal side effects were more common and sometimes led to discontinuation—particularly over longer follow‑up. (cochrane.org)
“These drugs have the potential to bring about substantial weight loss, particularly in the first year,” said Juan Franco, a co‑lead researcher at Heinrich Heine University Düsseldorf. Eva Madrid of Universidad de Valparaíso added: “We need more data on the long-term effects and other outcomes related to cardiovascular health, particularly in lower‑risk individuals… Weight regain after stopping treatment may affect the long‑term sustainability of the observed benefits.” (cochrane.org)
The authors note that most included trials were funded and operationally influenced by the manufacturers—raising conflict‑of‑interest concerns and underscoring the need for independent, longer‑term studies that assess outcomes beyond weight. Trials were conducted mainly in middle‑ and high‑income countries, with limited representation from regions such as Africa, Central America and Southeast Asia. (cochrane.org)
Regulatory context and access vary by country. In the United Kingdom, semaglutide (Wegovy) and liraglutide (Saxenda) are authorized for weight management, and tirzepatide (Mounjaro) has also been authorized for weight loss and weight management in adults alongside diet and physical activity. (gov.uk)
Affordability remains a barrier. Cochrane’s news materials point out that high prices for semaglutide and tirzepatide constrain access, while the expiration of liraglutide’s protections has allowed lower‑cost versions in some markets; in the United States, the FDA approved a generic version of Saxenda (liraglutide) in August 2025. Cochrane materials also state that semaglutide’s patent will expire in 2026, but patent protections differ by jurisdiction: analyses indicate that while some countries may see expirations around 2026, U.S. and European protections extend into 2031, delaying widespread generic competition. (cochrane.org)
The WHO commissioned the reviews to guide global recommendations. A draft WHO adult‑obesity guideline released for consultation in September 2025 signaled a conditional role for GLP‑1–based medicines alongside lifestyle support; the organization’s final guidance is expected to draw on these Cochrane findings. (cochrane.org)
