Why GLP-1 medications cause some people to lose more weight

According to a recent study, common DNA alterations can influence how much weight people lose while taking popular weight-loss medications like Ozempic or Mounjaro. The discovery recasts inconsistent outcomes and gastrointestinal side effects as part of the same biological narrative, pointing to the medications' own target receptors.

Why the outcomes vary

Weight loss varied from mild to significant in a survey of almost 28,000 users of these medicines. Based on such reports, researchers at the 23andMe Research Institute identified a receptor gene that is directly related to the way the medications work.

A slight gain that nevertheless demonstrated a distinct genetic advantage was associated with each copy of the important mutation, which was connected to an additional 1.7 pounds lost. The remainder of the picture still has to be filled in because that edge does not account for the majority of patient differences.

Where genes function

A small DNA alteration can modify the message that these medications convey because that receptor is located on cells that aid in appetite regulation. Instead of a remote helper pathway, the team discovered the signal in GLP1R, the gene that regulates the body's reaction to these medications.

It is simpler to link the variant to the drug's impact because that DNA alteration directly modifies the receptor's protein. The modified protein may enable more receptors to reach the cell surface, strengthening the medication signal, according to researchers.

Overlap of side effects

When the scientists examined individuals who reported feeling queasy or throwing up, one hint was found in the same DNA segment. Stronger receptor activity can cut both ways, as seen by signals close to GLP1R that were associated with those gastrointestinal side effects.

Individuals in the dataset who experienced more nausea or vomiting also tended to lose more weight while using these medications. That connection suggests that burden and benefit can share biology, but it does not imply that feeling ill is a good thing.

An additional receptor

Tirzepatide also triggers a second hormone route that can alter how the brain and stomach respond, in contrast to semaglutide, a medication that mimics a natural hormone to lower appetite.

Only tirzepatide increased the risk of vomiting in that additional pathway due to a variation in GIPR, a gene that aids cells in responding to a gut hormone associated with digesting. Instead than focusing on just one hormone system, this medication targets two.

Tirzepatide-induced vomiting was almost 15 times more likely in those with high-risk variants at both receptor genes. This drug-specific pattern is important because it distinguishes between tirzepatide and semaglutide stories rather than combining them.

Genetic influence limits

The analysis is cautious about the fact that genes were not the primary driver throughout. Genetics did not account for as much of the variation in weight reduction as sex, drug choice, dosage, duration of therapy, and diabetes status.

Participants with type 2 diabetes tended to lose less weight, whereas women tended to lose more. Because DNA only explains a portion of the story, this balance maintains the finding's usefulness and integrity.

Calculating the response to treatment

The team was able to categorise individuals into significantly distinct response groups after merging genes and medical histories. About 25% of the variation in weight loss across individuals was explained by that model, with non-genetic factors accounting for the majority of its power.

The team stated that estimated one-year results ranged from roughly 6% to 20% weight loss in a public blog. The same instrument showed a wide range of nausea or vomiting risk, from 5% to 78%.

Surveys supported by records

The study was made possible by survey responses, but the team faced a more difficult challenge with medical information. The two metrics moved in tandem when 195 individuals had both sources, but self-reported weight reduction continued to run higher.

Confidence in the outcome was bolstered when a different check in the NIH's All of Us program discovered the primary efficacy signal once more. Because people remember treatments differently and health records frequently overlook care taken elsewhere, that cross-check also revealed a limitation.

Increasing usage of certain medications

In the US, the use of GLP-1 receptor agonists—drugs that mimic gut signals and reduce appetite—has quickly expanded. Approximately one in eight American individuals, according to a national survey, had previously used one of these drugs.

Adults who were overweight or obese lost roughly 14.9% of their body weight after 68 weeks in a major semaglutide experiment. Response differences now matter so much since a major tirzepatide study increased average loss even further.

Current use limitations

Physicians are currently unable to determine the ideal medication, dosage, or rate for a single patient using a cheek swab. Nevertheless, in a discipline still dominated by trial and error, the paper describes precision medicine—treatment based on an individual's biology.

According to Dr. Adam Auton, Vice President of Human Genetics at 23andMe Research Institute, "identifying these variants in the GLP1R and GIPR genes provides an important new insight into why these medications impact people in distinct ways." Larger and more varied testing that demonstrates when genetics alters a prescription is now the most sensible next step.

The research's next steps

A clearer picture of why patients may experience the same well-known medications as potent, unsatisfactory, or unbearable is revealed. The potential will depend on demonstrating that these signals may provide more accurate guidance as datasets grow beyond primarily female and European samples.