Prof Loos said the genetic effect, while modest, “is similar to other factors – and not trivial”.
However she said the findings need to be reproduced in other studies and, to date, that has not happened.
For Dr Marie Spreckley, from the University of Cambridge, “genetics is only one part of a much more complex picture”.
She said the main drivers of outcomes are “behavioural, clinical, and treatment-related factors”. So how much daily exercise and healthy eating people do alongside taking the medication, as well as support and advice offered, plus other underlying health issues.
But there are other factors at play too.
Women are more than twice as likely to lose 15% of their body weight on Mounjaro than men, previous research suggests.
Being younger, white or Asian are also thought to be linked to more weight loss – although the reasons are not fully understood.
And the type of medication used, the dose and how long it is taken for have all been linked with greater weight loss.
In the long term, taking genetic and other information together could help guide the choice of which weight-loss drug to use, based on the potential benefits – something called “precision medicine”.
But we are not there yet, said Professor Naveed Sattar, metabolic health expert from the University of Glasgow.
“Overall, these findings are scientifically interesting, but they are a long way from changing clinical practice,” he said.
“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.”