Weight loss drugs like semaglutide and tirzepatide have changed the conversation around obesity. Some people drop pounds fast, while others see slower progress or struggle with side effects. This gap has puzzled doctors and patients alike.
A major study published in Nature now offers clearer answers. Researchers from the 23andMe Research Institute analyzed data from nearly 28,000 people. Their findings show that your genes may shape how well these drugs work and how your body reacts to them.
Your Genes Can Boost or Limit Results
David / Unsplash / The study found a genetic variant called rs10305420, located in the GLP-1 receptor gene. This gene controls how your body responds to drugs like semaglutide, which help you feel full sooner and eat less.
People who carry this variant tend to lose slightly more weight. On average, each copy of the variant led to about 0.76 kilograms of extra weight loss over eight months. Those with two copies lost even more. This happens because their satiety signals become stronger, making it easier to stop eating before overeating.
However, this does not mean the drug only works if you have this gene. It simply means some bodies respond more strongly than others. Think of it like turning up the volume on fullness signals. The drug still plays the same tune, but some people hear it louder.
Side Effects Also Have a Genetic Link
Another key discovery involves a different genetic variant, called rs1800437. This one sits in the GIP receptor gene, which plays a role in digestion and how the body handles certain hormones.
This variant does not affect weight loss directly. Instead, it affects how likely someone is to feel side effects like nausea and vomiting when taking tirzepatide. People with this variant may feel worse because their natural system that helps reduce nausea does not work as well.
In rare cases, people who carry high-risk variants in both genes faced a much higher chance of severe vomiting. The study found that the risk could jump up to 15 times higher. This shows that effectiveness and side effects can follow separate paths in the body.
Lifestyle Still Matters More Than You Think
Ketut / Pexels / The study confirmed that everyday factors still carry serious weight in how well these drugs work.
People who are younger, female, or who start with a higher body mass index often see better results. Those without type 2 diabetes also tend to lose more weight. The type of drug and the dose also shape outcomes in a big way.
Even with all this data, researchers found that genetics and lifestyle together explain only about 25% of the difference in results. That means most of the variation still comes from factors we do not fully understand yet, including diet habits, sleep, stress, and metabolism.
This research opens the door to more personalized care. Doctors may one day use genetic testing to guide treatment choices. Instead of trying different drugs blindly, they could predict which option will work best for each patient.
That could also help avoid unnecessary side effects. If someone has a higher risk of nausea, doctors might choose a different drug or adjust the dose early. This would save time and reduce frustration for patients.
Still, experts say it is too early to change medical practice based on this alone. The effects of these genes are real, but they are modest. The study also relied on self-reported data and mostly included people of European ancestry, which limits how widely the results apply.