Three major reviews commissioned by the World Health Organization have confirmed that GLP-1 receptor agonist medications like tirzepatide (Mounjaro and Zepbound), semaglutide (Ozempic and Wegovy), and liraglutide (Victoza and Saxenda) produce substantial weight loss, with some patients shedding up to 16 percent of their body weight. However, the same research highlights significant concerns about limited long-term safety data, common side effects, and the predominant role of drug manufacturers in funding and conducting the studies. How Much Weight Loss Can These Drugs Actually Deliver? The evidence is striking when it comes to short-term results. Tirzepatide, administered as a once-weekly injection, led to an average weight reduction of about 16 percent after 12 to 18 months based on data from 8 randomized controlled trials involving 6,361 participants. Semaglutide produced an average weight loss of roughly 11 percent after 24 to 68 weeks across 18 randomized controlled trials with 27,949 participants. Liraglutide showed more modest results, with average weight loss of about 4 to 5 percent based on 24 trials involving 9,937 participants. When compared head-to-head, tirzepatide outperformed semaglutide in clinical trials. In the SURMOUNT-5 trial, tirzepatide led to greater average weight loss at 72 weeks than semaglutide, with 20.2 percent weight loss compared to 13.7 percent, and more people reached deeper weight-loss thresholds of 10 percent, 15 percent, 20 percent, and 25 percent. In the pivotal SURMOUNT-1 trial, participants taking tirzepatide plus lifestyle changes lost on average about 15 percent of body weight at 5 milligrams, 19.5 percent at 10 milligrams, and 20.9 percent at 15 milligrams over 72 weeks, compared to roughly 3 percent with lifestyle changes plus placebo. "These drugs have the potential to bring about substantial weight loss, particularly in the first year. It's an exciting moment after decades of unsuccessful attempts to find effective treatments for people living with obesity," said Juan Franco, co-lead researcher from Heinrich Heine University Düsseldorf, Germany. Juan Franco, Co-lead Researcher, Heinrich Heine University Düsseldorf What Are the Major Safety Concerns Experts Are Raising? While the weight loss results are impressive, the WHO-commissioned reviews identified several troubling gaps in the evidence. Researchers found that when it came to major cardiovascular events, quality of life, or death, there was little or no difference between the GLP-1 drugs and placebo. This is particularly concerning given that these medications are being promoted as treatments for obesity-related health conditions. Side effects were more common with the medications than with placebo, particularly gastrointestinal issues. Common side effects include nausea, diarrhea, vomiting, constipation, abdominal pain, indigestion, injection-site reactions, fatigue, burping, hair loss, and reflux. These often occur during dose increases and may improve over time, but some participants discontinued treatment as a result. Less common but important risks have been observed with this drug class, including gallbladder problems such as gallstones or cholecystitis, kidney injury often related to dehydration from vomiting or diarrhea, and inflammation of the pancreas. Long-term safety data remain limited. Data from tirzepatide trials indicated that weight loss could last as long as 3.5 years, although information on long-term safety remains limited. Semaglutide findings suggest the effect can persist for up to two years, and evidence beyond two years of treatment for liraglutide was limited. The Industry Funding Problem: Why It Matters Perhaps the most significant concern raised by the WHO-commissioned reviews is the heavy involvement of pharmaceutical companies in the research itself. A large share of the studies included in the reviews were funded by the companies that manufacture the drugs. In many cases, the companies were deeply involved in designing, conducting, analyzing, and reporting the trials. This level of involvement raises serious concerns about potential conflicts of interest and underscores the need for more independent research. The researchers emphasized that longer-term, independently funded studies are crucial for guiding both medical practice and public health policy. A clearer understanding of sustained benefits and risks will help define the role of GLP-1 receptor agonists in long-term weight management. "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. More independent studies from a public health perspective are needed," explained Eva Madrid, co-lead researcher from the Universidad de Valparaíso, Chile. Eva Madrid, Co-lead Researcher, Universidad de Valparaíso Steps to Safely Use Weight Loss Medications If You're Considering Them - Slow Dose Escalation: Start at the lowest dose and increase gradually as prescribed. Slow, steady titration allows the gut to adapt and minimizes side effects. For Zepbound, you'll start at 2.5 milligrams once weekly for 4 weeks, then increase by 2.5 milligrams every 4 weeks or more as tolerated. - Dietary Adjustments: Favor smaller, protein-forward meals and limit high-fat foods, which can worsen nausea. These medications work best when combined with a reduced-calorie diet and increased physical activity, not as a standalone treatment. - Hydration and Monitoring: Stay well-hydrated to reduce dehydration-related risks from gastrointestinal side effects. If severe stomach pain occurs, especially with vomiting, or if mood changes or vision changes appear, call your clinician promptly. - Surgical Planning: Tell your surgical and anesthesia teams you're taking these medications before any procedures. Because these drugs slow stomach emptying, there's a precaution about pulmonary aspiration during anesthesia or deep sedation. - Avoid Compounded Versions: Use caution with unapproved or compounded versions of these drugs sold online. The FDA has warned that some have contained different chemical forms that are not the same as the approved drugs, or have led to dosing errors and adverse events. What Happens When You Stop Taking These Medications? One critical issue that deserves attention is weight regain after stopping treatment. In a randomized withdrawal study called SURMOUNT-4, participants who switched from tirzepatide to placebo after significant weight loss regained weight, while those who continued treatment maintained or lost more. This pattern mirrors what we see with other obesity medications, suggesting that long-term weight maintenance hinges on ongoing treatment and strong lifestyle routines. This raises important questions about the sustainability of these treatments and whether they represent a long-term solution or a medication that must be taken indefinitely to maintain results. Access and Equity: Who Can Actually Get These Drugs? The authors of the WHO-commissioned reviews stress that broader use of GLP-1 medications must account for social and commercial determinants of health, such as cost, insurance coverage, and overall access. Without careful planning, expanded use could worsen existing health disparities among people living with obesity. High prices currently restrict access to semaglutide and tirzepatide, while liraglutide has become more affordable after its patent expired, allowing generic versions to enter the market. Semaglutide's patent will also expire in 2026, which may increase access to that medication. Insurance coverage for these medications varies widely by plan, making it difficult for many people to access them. Additionally, most of the trials reviewed were conducted in middle- and high-income countries. Regions including Africa, Central America, and Southeast Asia were underrepresented or not represented at all. Because body composition, diet, and health behaviors vary widely across populations, researchers emphasize the importance of studying how these drugs perform in diverse global settings. The WHO-commissioned reviews conclude that these findings will inform new WHO guidelines on the use of GLP-1 receptor agonists for obesity treatment. However, the research makes clear that while these medications offer genuine benefits for weight loss, significant questions remain about their long-term safety, the independence of the research supporting them, and whether they represent a sustainable solution for obesity management across diverse populations worldwide.
