A fresh wave of research is shedding light on a question millions have been asking. Why do some people see dramatic results from weight-loss injections, while others barely notice a change? The answer, it turns out, may lie partly in genetics, but that is only one piece of a much bigger puzzle.

Genes May Influence Weight-Loss Results

Researchers have identified variations in two specific genes linked to appetite and digestion that appear to impact how well weight-loss drugs work. These medications, including widely used options like Wegovy and Mounjaro, mimic natural hormones in the gut that signal fullness, helping users eat less.

However, the study suggests that not everyone responds equally. Some individuals with certain genetic variants tend to lose more weight, while others experience stronger side effects.

Professor Ruth Loos, from the University of Copenhagen, explained:
“The study found a genetic variant associated with weight loss, which was also associated with nausea.

“People lose more weight if they have this variant.”

Interestingly, those carrying two copies of the gene may see even greater results, effectively doubling the additional weight loss compared to others.

The Numbers Behind The Findings

The study analyzed data from 15,000 people using weight-loss medications over roughly eight months. On average, participants lost 11.7% of their body weight.

Yet the range was striking. Some individuals lost as much as 30%, while others saw little to no change at all.

Clinical trials have previously shown higher averages, around 14% weight loss with semaglutide and up to 20% with tirzepatide. Still, real-world results often vary, and this research helps explain why.

Side Effects May Also Be Genetic

While greater weight loss might sound appealing, there is a trade-off. The same genetic factors linked to better results may also increase the likelihood of unpleasant side effects.

Another gene variant identified in the study appears to raise the risk of severe nausea and vomiting, particularly with tirzepatide. In rare cases, about 1% of users could experience vomiting at levels far worse than typical reactions.

That raises an important question. Are stronger results worth harsher side effects? For many, the answer will depend on individual tolerance and medical guidance.

Not Just About DNA

Despite the genetic connection, experts caution against viewing DNA as the sole driver of outcomes.

Dr Marie Spreckley, from the University of Cambridge, emphasized:
“genetics is only one part of a much more complex picture”.

She pointed to lifestyle and medical factors as key influences, adding that the main drivers include “behavioural, clinical, and treatment-related factors”.

In other words, diet, exercise, medical history, and support systems still play a major role in determining success.

Other Factors That Shape Results

Beyond genetics, several patterns are beginning to emerge.

Women appear more than twice as likely as men to lose 15% of their body weight on certain medications. Age also matters, with younger individuals often seeing better outcomes.

Ethnicity may influence results too, although researchers are still working to understand why. Additionally, the type of drug, dosage, and treatment duration all contribute to how effective the therapy is.

Meanwhile, access remains uneven. Although around 1.6 million people in the UK are believed to have tried weight-loss drugs in the past year, most obtain them privately. Public healthcare access is still limited to specific high-risk cases.

The Future Of Personalized Treatment

Looking ahead, researchers believe these findings could pave the way for more personalized treatment approaches.

By combining genetic data with lifestyle and clinical factors, doctors may eventually tailor weight-loss therapies to each individual, an approach known as precision medicine.

Still, experts urge caution.

Professor Naveed Sattar, a metabolic health specialist, said:
“Overall, these findings are scientifically interesting, but they are a long way from changing clinical practice,”

“What we really need now is more robust trial data to better define the balance of benefits and harms with these and many other emerging newer therapies.”

For now, the takeaway is clear. While genetics may tilt the odds, success with weight-loss jabs depends on far more than DNA alone.