Ozempic Muscle Loss: What the Body-Scan Data Show

Ozempic muscle loss is real but often overstated. When people lose weight on semaglutide (Ozempic, Wegovy) or tirzepatide (Mounjaro, Zepbound), part of what they lose is lean tissue, not just fat. In a body-scan substudy of the STEP 1 trial, about 38% of the weight lost was lean mass, and in the SURMOUNT-1 tirzepatide trial the figure was about 25%. Lean mass is not the same as muscle: it also includes water, organs and other non-fat tissue, and a 2025 nutrition advisory estimates that roughly half of it is muscle. The labels themselves state that these medicines reduce fat mass more than lean mass. The most consistently supported ways to protect muscle are regular strength training and enough protein, planned with a clinician, especially for older adults.

Peptide Labs does not sell Ozempic, Wegovy, Mounjaro, Zepbound or any prescription drug. This article summarizes FDA labels and published research. For the other effects reported across the class, see our guide to GLP-1 medicine side effects.

Does Ozempic muscle loss really happen?

Yes, in the sense that lean mass goes down. Any large weight loss removes some lean tissue along with fat, and GLP-1 medicines produce large weight losses. The Wegovy and Zepbound prescribing information (revised June 2026 and August 2026) both say the medicine lowers body weight with greater fat mass loss than lean mass loss. The Foundayo label (July 2026) says the same. The open question is how much of the lean loss is muscle, and whether it affects strength and daily function.

Trials measure this with dual-energy X-ray absorptiometry (DXA), a low-radiation scan that splits the body into fat, lean soft tissue and bone. DXA cannot tell muscle apart from other lean tissue, such as fluid and organs. A 2024 review in Diabetes, Obesity and Metabolism points out that lean mass includes muscle, organs, bone, fluids and even the water inside fat tissue, so a drop in lean mass is not a one-to-one drop in muscle.

GLP-1 muscle loss in the trials: what DXA scans found

The table summarizes the main body-composition data for GLP-1 muscle loss. All figures are averages, and the substudies were small subsets of much larger trials.

A 2025 joint advisory from four U.S. nutrition and obesity societies worked through the STEP 1 numbers: of an average 13.6 kg lost, 8.3 kg (62%) was fat and 5.3 kg (38%) was lean mass. Because muscle is about half of lean mass, the advisory estimates that roughly 20% of the total weight lost was muscle. Results vary between studies. The 2024 review notes reported lean losses ranging from 40% to 60% of weight lost in some studies to about 15% or less in others.

Lean mass loss on Wegovy compared with dieting

Lean mass loss on Wegovy and similar medicines is not unique to the drugs. The SURMOUNT-1 authors note that diet-restriction studies commonly report about 75% of weight lost as fat and 25% as lean mass, and in their own substudy the placebo group, who lost much less weight, showed the same 75/25 split as the tirzepatide group. The advisory adds that the losses are similar to those seen after bariatric surgery and very low-calorie diets.

Because fat falls faster than lean tissue, body composition usually improves. In STEP 1 the lean share of body weight went up, not down, and the 2026 meta-analysis found the same pattern across trials. Imaging studies with MRI, discussed in the 2024 review, suggest that muscle quality may improve as fat stored inside the muscle decreases. These are encouraging signals, but most participants were middle-aged and fairly healthy, and few trials measured strength or physical function directly.

Who should pay closer attention

The advisory says low protein intake from reduced appetite may add to muscle loss and the risk of sarcopenia (age-related loss of muscle mass and strength), particularly in people who are:

• Older adults, especially those already frail or at risk of falls.
• Perimenopausal or postmenopausal women, or men with low testosterone.
• Inactive, or not doing any resistance or strength training.
• Eating very little because of strong appetite suppression, nausea or other digestive side effects.
• Living with type 2 diabetes or another chronic illness, which the advisory lists as sarcopenia risk factors.

For these groups, the SURMOUNT-1 authors note that losing lean mass may be undesirable for older adults with or at risk of sarcopenic obesity, even though the share of lean loss was similar in people 65 and older. A clinician can assess strength and function before and during the medicine.

How to prevent muscle loss on Ozempic: what the evidence supports

Nobody can promise zero lean loss, but the research is fairly consistent on how to prevent muscle loss on Ozempic as far as possible. These points come from the 2025 joint advisory:

• Strength training. The advisory calls structured resistance training, or resistance plus aerobic exercise, well established for preserving lean mass during weight loss, and notes that aerobic exercise alone has a smaller effect. It suggests strength training at least three times a week plus at least 150 minutes of moderate aerobic activity, adapted to each person’s fitness.
• Protein at regular meals. It emphasizes protein and minimally processed foods, and regular small meals rather than long gaps. Individual protein needs vary with body size, age and kidney health, so a registered dietitian can set a personal target. Our eating guide for GLP-1 medicines has practical meal ideas.
• Steady, not extreme, calorie cuts. The advisory says lean loss depends partly on how severe the calorie restriction is and how fast weight comes off. Eating very little because appetite has vanished can work against muscle.
• Supplements only when needed. The advisory mentions protein or micronutrient supplementation as needed under clinical care. Food comes first, and no supplement has been shown to replace exercise for preserving muscle.

Exercise may help bone as well. The advisory cites a randomized trial in which a year of GLP-1 therapy plus exercise preserved bone mineral density, while the medicine alone reduced it. If you feel weak or unusually tired, see our guide to tiredness on GLP-1 medicines; low food intake and dehydration are common contributors.

Muscle, plateaus and peptide marketing

A smaller body, with less fat and somewhat less lean tissue, needs fewer calories, one of several reasons weight loss slows over time. Our article on why weight loss stalls explains the wider picture, and typical results in GLP-1 trials shows how weight curves level off.

Online, muscle loss on GLP-1 medicines is often used to sell research peptides labeled not for human use. These products are not FDA-approved for building or preserving muscle; our explainer on what the evidence and the FDA say about muscle peptides covers why. Drugs designed to protect muscle alongside GLP-1 medicines are being studied, but none is FDA-approved for that purpose.

Frequently Asked Questions

Peptide Labs does not sell GLP-1 medicines or any prescription drug. This article is general information, not medical advice. Read the Medication Guide that comes with a prescription, and ask a pharmacist or prescriber how this information applies to you.

Last reviewed October 2026.

Related guides: GLP-1 Diet: What Experts Recommend While on GLP-1 Medicines, GLP-1 Fatigue: Why You Feel Tired and What Helps, GLP-1 for Weight Loss: What the Trials Actually Showed, Ozempic Butt: Why Weight Loss Changes Your Shape, Creatine for Weight Loss: Water Weight, Fat Loss and Muscle.