Muscle loss on Ozempic is becoming an increasingly important topic as more Australians use GLP-1 medications such as Ozempic (semaglutide) and Mounjaro (tirzepatide) for weight loss. While these medications can be highly effective, many people are surprised to learn that rapid weight loss may also lead to a loss of muscle mass if it is not managed properly. At BeFit Training Physiotherapy, we help people prevent muscle loss through evidence-based strength training, body composition assessment and personalised exercise programmes that support healthy, sustainable weight loss.
The short answer is that most of the weight lost is fat. But the longer answer is more nuanced — and it has real implications for your strength, your metabolism, and how you age.
What Are GLP-1 Medications?
GLP-1 receptor agonists are a class of medication originally developed to manage type 2 diabetes. They work by mimicking a hormone that regulates blood sugar and appetite, which leads to reduced food intake and meaningful weight loss.
The best-known GLP-1 drug in Australia is semaglutide, sold under the brand names Ozempic (for type 2 diabetes) and Wegovy (for weight management). Tirzepatide — sold as Mounjaro — works on both the GLP-1 and GIP receptors, making it a dual agonist and, in most studies, the more potent option for weight loss.
Ozempic has been on the Pharmaceutical Benefits Scheme (PBS) for type 2 diabetes since 2020 and remains PBS-subsidised for that indication at around $31.60 per script. Mounjaro is registered in Australia for diabetes and weight management but is not currently PBS-subsidised for weight loss, making it a private prescription at significantly higher cost. Wegovy was recommended for PBS listing by the Pharmaceutical Benefits Advisory Committee (PBAC) in November 2025, for adults with established cardiovascular disease and obesity, though that listing is not yet finalised as of mid-2026.
Do GLP-1 Drugs Cause Muscle Loss?
This is the question everyone taking these medications — or thinking about it — wants answered.
The research suggests that GLP-1 drugs do not directly cause muscle wasting in the way that illness or prolonged immobilisation does. However, some lean mass loss does occur alongside fat loss, and in some patients, the proportion is clinically meaningful.
Here is what the major studies show:
Across large clinical trials, approximately 25% to 40% of the total weight lost on semaglutide (Ozempic/Wegovy) has been attributed to lean mass, with the remainder coming from fat. In the STEP 1 trial for semaglutide, participants lost an average of 15.2 kg, of which around 6.9 kg was lean mass — nearly 45% of total weight lost.
Tirzepatide (Mounjaro) drives greater total weight loss than semaglutide, but the proportion of lean mass lost appears similar. Because Mounjaro users lose more weight overall, they tend to lose more absolute kilograms of muscle. A large real-world study published in early 2026 found that tirzepatide was associated with 2% greater lean body mass loss than semaglutide by 12 months. That same study found that people with pre-existing musculoskeletal pain — including knee pain and neck pain — lost significantly more lean tissue, regardless of which drug they were taking.
Importantly, some degree of lean mass loss is normal during any meaningful weight loss, whether from diet, surgery, or medication. The concern with GLP-1 drugs is that the scale of weight loss is larger than most people achieve through lifestyle changes alone, meaning the absolute amount of lean tissue lost can be more significant.
Why Does Muscle Loss Matter?
Muscle is not just about appearance. It is metabolically active tissue that plays a central role in insulin sensitivity, bone health, balance, and long-term functional capacity.
When muscle mass declines, the risks include:
Sarcopenia — the progressive loss of muscle mass and strength that accelerates after age 50 and is linked to falls, fractures, hospitalisation, and reduced independence. GLP-1 medications are being used by an increasingly older population, and this group has less lean tissue reserve to begin with.
Metabolic slowdown — muscle burns more energy at rest than fat does. Losing lean tissue can reduce resting metabolic rate, which makes long-term weight maintenance harder once medication is stopped or reduced.
Bone density decline — a 2025 review published in Frontiers in Aging noted that musculoskeletal risks are an emerging concern with pharmacologic weight loss, particularly in older adults at risk of sarcopenia or frailty.
Reduced physical function — the largest study to date on real-world GLP-1 users found that reduced exercise tolerance was the strongest correlate of greater lean body mass loss. In other words, patients who became less active during treatment lost significantly more muscle.
The Most Important Thing You Can Do
The evidence here is clear, consistent, and directly actionable.
Resistance training is the most effective strategy for preserving muscle mass during GLP-1 therapy.
A review published in Obesity Reviews in 2025, examining strategies for minimising muscle loss during GLP-1 treatment, concluded that structured resistance exercise — combined with adequate protein intake — has significant potential to preserve lean mass and offset the muscle changes typically seen with these medications.
This is not a minor footnote. It means the clinical value of GLP-1 medication is substantially improved when it is paired with a well-designed exercise program. It also means that doing nothing, or only light walking, is a missed opportunity at best and a risk to long-term health at worst.
What Does a Good Exercise Program Look Like on GLP-1 Medication?
Not all exercise is equally effective for preserving muscle during weight loss. A few principles matter:
Progressive resistance training. This means lifting weights or using resistance in a structured, progressive way — increasing load over time as strength improves. Research consistently shows this is the most effective intervention for maintaining lean mass during caloric restriction.
Frequency and consistency. Most evidence points to two to three resistance sessions per week as a meaningful minimum. The goal is not intensity for its own sake — it is consistent stimulus to the muscles across the week.
Protein intake. Resistance training works best when paired with adequate protein. Your GP or a dietitian can advise on appropriate targets for your circumstances.
Starting before you lose the weight. Ideally, an exercise program is established before or alongside GLP-1 treatment — not added later as an afterthought. The earlier the stimulus, the more lean tissue is preserved throughout the weight loss process.
If you have existing musculoskeletal pain — which, as the research shows, significantly increases lean tissue loss during GLP-1 therapy — this makes physiotherapy-led exercise assessment even more important. Knee pain, back pain, or hip problems should not be a reason to avoid resistance training; they are a reason to have it supervised and individualised.
How a Physiotherapist Can Help
A physiotherapist with experience in exercise prescription and body composition can support your GLP-1 journey in several practical ways.
Movement assessment. Before building a strength program, it helps to understand how you currently move — where there are restrictions, compensations, or areas of weakness that need to be addressed first.
Individualised exercise prescription. A structured program tailored to your starting point, your goals, and any existing injuries or conditions. Not a generic gym routine — a program built around your body.
Body composition tracking. At BeFit’s Edgecliff clinic, DEXA scanning is available to provide an objective measure of lean mass, fat mass, and bone density. For anyone on GLP-1 medication, this gives a clear baseline and the ability to track what is actually changing over time — not just weight on a scale.
Progressive loading. As fitness improves and weight changes, the program should be updated regularly. A physiotherapist can guide this progression in a way that is safe and effective.
Frequently Asked Questions
Can I exercise while taking Ozempic or Mounjaro?
Yes. Exercise is not only safe while taking GLP-1 medications — it is strongly recommended. Resistance training in particular helps preserve the muscle mass that would otherwise be lost during weight loss.
How much muscle will I lose on Ozempic?
This varies significantly between individuals. Clinical trials suggest that lean mass accounts for roughly 25% to 45% of total weight lost on semaglutide. The amount can be meaningfully reduced with structured resistance training and adequate protein intake.
Is Mounjaro worse for muscle loss than Ozempic?
The proportion of lean mass lost appears similar between the two drugs. However, because Mounjaro drives greater total weight loss, users tend to lose more absolute muscle. People with pre-existing musculoskeletal pain appear to be at higher risk of lean tissue loss on either medication.
Do I need a referral to see a physiotherapist about exercise on GLP-1 medication?
No referral is needed to book an assessment at BeFit. You can contact either our Edgecliff or Coogee clinic directly.
What is a DEXA scan and is it worth having?
A DEXA scan measures your body composition, including lean mass, fat mass, and bone density. For someone taking a GLP-1 medication, it provides an objective baseline and allows you to track what is changing over time — beyond what the scales can show. DEXA scanning is available at BeFit’s Edgecliff clinic.
Will my private health insurance cover physiotherapy?
Most private health insurance extras policies include physiotherapy. Check the details of your cover for consultation and exercise physiology rebates.
A Note on the Bigger Picture
GLP-1 medications represent a genuine shift in how type 2 diabetes and obesity are managed. For many people, they are a meaningful clinical tool — one that is improving health outcomes and quality of life.
The goal of this article is not to create concern about these medications, but to make the case for using them as part of a comprehensive approach to health — one that includes structured exercise, appropriate nutrition, and regular monitoring of what is actually happening to your body composition over time.
The people doing best on GLP-1 therapy, based on the emerging evidence, are those who stay active, maintain a resistance training habit, and work with health professionals who can support the whole picture — not just the number on the scale.
Book an Assessment at BeFit
If you are taking Ozempic, Mounjaro, or another GLP-1 medication and want to build a structured exercise program around it, our team at BeFit Training Physiotherapy can help.
Both our Edgecliff and Coogee clinics offer physiotherapy-led exercise assessment and prescription. DEXA body composition scanning is available at our Edgecliff clinic for those who want objective data to guide their program.
No referral required. Contact us to book an initial assessment.
