Weight-loss medicines such as semaglutide and tirzepatide have become some of the most talked-about drugs in the world. Their brand names, including Ozempic, Wegovy, Rybelsus, Mounjaro, and Zepbound, are now familiar to millions of people.
They are often described as breakthrough treatments because many patients have achieved weight loss that was previously difficult to reach without surgery.
These medications belong to a newer group of drugs called GLP-1 receptor agonists. They work by copying natural hormones that help control appetite, slow stomach emptying, and make people feel full for longer periods of time. As a result, many people eat less and gradually lose weight.
However, doctors have noticed an interesting pattern. Some patients lose a large amount of weight, while others lose very little. Until now, there has been limited information about how much these responses can vary in everyday life.
To answer this question, researchers led by Venky Soundararajan examined anonymous electronic health records from more than 20,000 patients. The scientists studied two carefully matched groups. One group included 10,339 people taking tirzepatide, while the other included 10,339 people taking semaglutide.
Their findings were published in the journal PNAS Nexus.
The results showed that there is no single response to these medicines. Weight loss ranged from almost no change at all to reductions of more than one-quarter of a person’s body weight. This means that two people taking the same drug may have very different experiences.
On average, people taking tirzepatide lost more weight than those taking semaglutide. The tirzepatide group lost an average of 14.7 percent of their body weight, while the semaglutide group lost about 10.8 percent.
The researchers also looked at people they called high responders. These were patients who lost more than 15 percent of their body weight in one year. They found that nearly twice as many people taking tirzepatide reached this level of weight loss compared with those taking semaglutide.
The study also examined side effects. Many people worry about stomach problems, tiredness, headaches, and other unpleasant symptoms when starting these medicines. The researchers found that people taking tirzepatide generally experienced fewer stomach-related problems, headaches, and fatigue than those taking semaglutide.
The study also uncovered differences among groups of patients. Women and white patients were more likely to experience significant weight loss with both medications. In contrast, men, Black patients, and Hispanic patients were more likely to lose less than 5 percent of their body weight during a year of treatment.
The reasons for these differences are still unknown. The researchers say more studies are needed to understand why people from different backgrounds respond differently to these medications. Many factors may play a role, including biology, genetics, diet, lifestyle, other medical conditions, and differences in healthcare access.
The findings also highlight an important message for patients. Although these medicines can be very effective, they are not magic treatments that work exactly the same way for everyone.
Expectations should be realistic. Some people may experience dramatic changes, while others may need additional support through dietary changes, physical activity, and long-term medical guidance.
The study is important because it used information from real patients rather than the highly controlled environment of a clinical trial. Real-world studies often provide a clearer picture of what doctors and patients can expect in everyday medical practice.
The results suggest that tirzepatide may provide greater average weight loss than semaglutide and may also cause fewer common side effects.
However, the findings also remind us that weight loss is highly individual. Doctors may eventually need more personalized approaches to help determine which medicine is most suitable for each patient.
The study findings are encouraging because they show that these medications can produce substantial weight loss for many people.
At the same time, they raise important questions about why responses differ so much between individuals and demographic groups. Future research may help doctors predict who is most likely to benefit from each treatment and improve weight-loss care for everyone.
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Source: Harvard Medical School.
