The weight loss drug craze has thrown up many questions – some more anxiety-ridden than others. But one of the most prominent is: can you still exercise while on Mounjaro, or other such drugs like Ozempic?

Originally used to fight diabetes, these drugs suppress your appetite by mimicking the hormone called GLP-1 (glucagon-like peptide-1), which plays a key role in how the body processes food. Basically, it casuses users to eat less. Based on the calories in – calories out metric, aka the cornerstone of weight loss, you’ll naturally start to lose weight.

What’s less clear-cut is how much exercise you need to do. Can you tear up your gym membership and throw your running trainers in the bin after your first Mounjaro injection? Could it be harmful to keep smashing HIIT classes? Or should you step up your workouts so you’re burning even more calories and supercharging your weight loss? We’ve got the answers.

Do weight loss drugs actually burn fat?

Not directly. Rather, they work by quieting ‘food noise’ in your head, enabling you (in theory) to make healthier food choices. Love reaching for a Mars Bar in the evening? These drugs can help you resist the urge.

“GLP-1 receptor agonists like semaglutide, liraglutide, and tirzepatide [i.e. the active substance in weight loss drugs] work by suppressing appetite rather than directly increasing fat burning,” explains PT Adam Enaz. “This appetite reduction leads to a calorie deficit, which drives weight loss.”

How this works is actually pretty simple: When you’re in a calorie deficit, especially one driven by eating less (as with GLP-1s), the body taps stored fat for energy, particularly during exercise. With less readily available energy from recent food, the body mobilises stored fat as fuel.

Taking Mounjaro is not your cue to stop exercising for good

“Because GLP-1 medications such as semaglutide mainly curb appetite and not metabolism, physical activity is indispensable to preserve your muscle mass and keep your metabolism up and running,” says expert PT Farren Morgan. “In fact, people taking these drugs can lose up to 25 to 40 percent of their lean muscle mass if they aren’t doing anything to maintain it.”

There’s scientific evidence to support this. Morgan points to a July 2025 report published in the Journal of the American Medical Association titled ‘Integrating Diet and Physical Activity When Prescribing GLP1s—Lifestyle Factors Remain Crucial.’

“The study authors came up with a structured approach to maintaining muscle mass and fitness during GLP1 use,” Morgan explains. “The authors suggest users should start with daily low-intensity movement, then transition to resistance training (60 to 90 minutes per week). After that, it’s recommended to progress to regular aerobic exercise, like steady state jogging (30 to 60 minutes per day). By combining cardio with weight training, you’ll support weight loss, while providing enough stimulus to ensure your muscles still grow.”

“The data is pretty clear,” adds nutritionist Gráinne Quinn Jordan. “Exercise and medication together give the best outcomes. Weight loss drugs like semaglutide and liraglutide will help you lose weight on their own, but people who add in regular movement lose a greater proportion of fat, hold onto more muscle, and are more likely to keep the weight off once the medication stops.”

In one trial, people were followed for a year after stopping liraglutide. Those who combined the drug with structured exercise kept far more of the weight off than those who hadn’t exercised. So the drug does its job, but it’s movement that makes the difference long term.