New light shed on who benefits most from weight-loss jabs

A recent study indicates that individuals with specific genetic markers linked to hunger and digestion may experience greater weight loss when using drugs like Wegovy and Mounjaro. Published in the *Nature* journal, the research highlights how these genetic differences could explain varying responses to obesity treatments, including differences in effectiveness and side effects such as nausea or vomiting.

Drug Mechanism and Weight Loss Outcomes

These medications work by mimicking a natural gut hormone that suppresses appetite, making users feel satiated. However, the amount of weight lost can differ significantly among patients. Trials show semaglutide (Ozempic, Wegovy) typically leads to around 14% weight reduction, while tirzepatide (Mounjaro) can result in up to 20%. In a study of 15,000 participants, the average loss was 11.7% over eight months, with some achieving 30% reduction and others gaining little or nothing.

Genetic Variants and Their Impact

Participants in the study had previously undergone genetic testing via 23andMe, allowing researchers to analyze millions of genetic markers. They identified a variant associated with weight loss and nausea, suggesting that people carrying this gene may lose additional weight—about 0.76kg (1.6 lbs) on average. Those with two copies of the gene could see double the benefit. The variant is more common in individuals of European descent, with 64% having one copy and 16% having two, compared to 7% among African Americans.

“The study found a genetic variant associated with weight loss, which was also linked to nausea. People lose more weight if they have this variant,” said Professor Ruth Loos of the University of Copenhagen.

Other Contributing Factors

While genetics play a role, experts emphasize that factors like sex, age, and ethnicity also influence outcomes. Dr. Marie Spreckley from the University of Cambridge noted that “genetics is only one part of a much more complex picture,” with behavioural, clinical, and treatment-related factors being key. For instance, women are more than twice as likely as men to lose 15% of their body weight on Mounjaro, though reasons for this are not fully clear.

Future Implications and Challenges

The study’s findings could pave the way for “precision medicine,” where genetic and personal data guide drug selection. However, Professor Naveed Sattar from the University of Glasgow cautioned that “these findings are scientifically interesting, but a long way from changing clinical practice.” He stressed the need for further trials to better understand the balance of benefits and risks for these and other newer therapies.

Usage Trends in the UK

Approximately 1.6 million people in the UK have used weight-loss drugs in the last year, with numbers rising. Most are purchased privately through online pharmacies, while the NHS provides Wegovy and Mounjaro to only a small fraction of patients with severe obesity and related conditions.