How to prevent muscle loss on Mounjaro

If you're taking Mounjaro to lose weight, you probably want to lose body fat without sacrificing your strength or muscle mass. But when the number on the scales starts falling, how can you be sure you're losing the right kind of weight?

Weight loss often involves a reduction in both body fat and lean mass, which includes muscle. Research into tirzepatide, the active ingredient in Mounjaro, has found that people lose some lean mass during treatment, although fat accounts for a much greater proportion of the weight lost.

In this guide, we'll explore why muscle loss can happen while taking Mounjaro, what the research tells us, and how nutrition, strength training, and the right support can help you protect your muscles as you lose weight.

Does Mounjaro cause muscle loss?

Yes, some muscle loss can occur while taking Mounjaro, although this is generally associated with weight loss rather than the medication directly damaging muscle tissue.

In the SURMOUNT-1 body composition study, researchers found that approximately 75% of the weight participants lost during tirzepatide treatment came from fat mass, while around 25% came from lean mass.

However, lean mass isn't the same as muscle mass. It also includes water, organs, and other non-fat tissues, so these findings don't mean that a quarter of the weight lost was muscle.

Maintaining muscle matters because it supports your strength, mobility, and ability to carry out everyday activities.

Does Mounjaro eat away at muscle?

No. There's no established evidence that Mounjaro directly breaks down or destroys muscle tissue.

Instead, muscle loss with Mounjaro is a potential consequence of weight reduction, particularly if you're not eating enough or maintaining regular physical activity.

Why can you lose muscle while taking Mounjaro?

Mounjaro helps reduce appetite and food intake, making it easier to lose weight. However, the changes that help you lose body fat can also make it harder to maintain muscle, particularly if you're eating less or becoming less active.

Several factors can contribute to muscle loss during treatment.

Losing a substantial amount of weight

When you lose weight, your body doesn't exclusively use stored fat for energy. Some lean mass may also be lost, particularly during substantial weight reduction.

The SURMOUNT-1 study found that participants taking tirzepatide lost both fat and lean mass. However, it didn't establish that faster weight loss necessarily causes greater muscle loss.

Not getting enough protein

Protein provides the building blocks your body needs to maintain and repair muscle tissue. If Mounjaro significantly reduces your appetite, you might find yourself eating smaller portions and so struggling to get enough protein.

Not using your muscles regularly

Research has shown that resistance exercise can help preserve lean mass and improve strength during weight loss. Activities such as lifting weights or using resistance bands can help you maintain your muscles as your weight decreases.

Not eating enough calories on Mounjaro

Eating fewer calories is an important part of weight loss, but consistently eating too little can make it difficult to meet your body's nutritional needs. If you're regularly skipping meals or struggling to eat because you feel full, you may notice being too tired to train properly. Alongside not consuming enough protein, this can, in time, cause you to lose muscle mass.

How to prevent muscle loss on Mounjaro

Although some loss of lean mass can happen during weight loss, there are steps you can take to help protect your muscles while taking Mounjaro. The key is to combine good nutrition with regular physical activity, rather than focusing solely on the number on the scales.

“If you're worried about losing muscle while taking Mounjaro, remember that it's not just about how much weight you lose, but how you lose it. Eating enough protein, staying active, and including some strength training in your routine can all help protect your muscles. You don't need to make big changes overnight. Start with what feels manageable and build from there.”

Ayesha BashirPrescribing Pharmacist

Make strength training part of your routine

Resistance exercise is one of the most effective ways to preserve muscle during weight loss. Research suggests that strength training helps reduce the loss of lean mass while improving muscle strength.

You don't need to join a gym to get started. Bodyweight exercises, resistance bands, and light dumbbells can all help. Aim to include muscle-strengthening activities at least twice a week, gradually increasing the difficulty as your fitness improves.

Prioritise protein at every meal

Your body needs protein to maintain and repair muscle tissue, particularly when you're losing weight. Try including a protein source with each meal, such as eggs, fish, chicken, beans, lentils, or yoghurt.

Avoid eating too little

Mounjaro can make you feel full after smaller meals, but it's still important to eat enough to meet your nutritional needs.

Rather than skipping meals or trying to lose weight as quickly as possible, focus on regular, balanced meals that provide protein, carbohydrates, healthy fats, and essential vitamins and minerals. If you struggle to get in enough food throughout the day, read our guide to how to eat well when your appetite is low.

Stay active between workouts

Strength training is important, but everyday movement also helps maintain your physical fitness and independence.

Walking, cycling, swimming, and other activities you enjoy can support your overall health while you're losing weight. Try to build movement into your daily routine in ways that feel manageable and sustainable.

Monitor your strength, not just your weight

The scales can't tell you how much of your weight loss comes from fat or muscle. That’s why it’s important to pay attention to how you're feeling and performing during everyday activities. Think about everyday things like carrying your shopping, climbing the stairs, getting up from a chair or completing your usual workout. If these activities start to feel noticeably harder, or you feel weaker than usual, it could be a sign that your strength is changing.

Can you gain muscle on Mounjaro?

Yes, building muscle on Mounjaro is certainly possible. Although losing weight can involve a reduction in lean mass, this doesn't mean you can't improve your strength or build muscle while taking the medication.

Building muscle on Mounjaro

If you're hoping to maintain or gain muscle during treatment, focus on a few practical habits:

• Train regularly: Include resistance exercises such as squats, press-ups, weightlifting, or resistance band workouts.
• Eat enough protein: Include protein-rich foods throughout the day to support muscle repair and growth, even if your appetite is reduced.
• Avoid excessive calorie restriction: Even though the medication will naturally reduce your appetite, losing weight doesn't mean eating as little as possible. Make sure you're getting enough energy and nutrients to support your activity and help you feel comfortable day-to-day.
• Allow time for recovery: Give your muscles time to recover between challenging workouts, particularly when you're starting a new exercise routine.
• Consider creatine: Creatine may help improve strength and exercise performance when combined with resistance training, although its benefits specifically for people taking Mounjaro haven't been established. Speak to your healthcare team before using it.

Does Mounjaro cause muscle pain?

Muscle pain and muscle aches aren't listed as common side effects in the official Mounjaro product information. However, you may still experience muscle discomfort while taking the medication.

If you've recently started exercising or increased the intensity of your workouts, you might experience delayed onset muscle soreness (DOMS). This can cause aching and stiffness after unfamiliar or challenging physical activity, particularly when you're introducing strength training.

Speak to your pharmacist or healthcare team if you're experiencing persistent, unexplained, or worsening muscle pain.

Protecting your muscles while losing weight

Losing weight on Mounjaro doesn't have to mean sacrificing your strength. Although some reduction in lean mass is common during weight loss, regular strength training, adequate protein intake, and a balanced diet can help protect your muscles. The key is to focus on more than the number on the scales.

Getting support throughout your treatment

Maintaining your strength and muscle mass is an important part of healthy weight loss. If you're concerned about muscle loss on Mounjaro, or finding it difficult to eat enough during treatment, you don't have to manage these challenges alone.

At myBMI, our treatment plans include ongoing clinical support to help you manage your weight loss safely and sustainably. Our clinical team can offer guidance if you're struggling with your appetite, nutrition, or other treatment-related concerns. We also provide free medication to help manage certain side effects, if deemed appropriate.

For more information about what to expect during treatment, explore our guide to Mounjaro side effects.

With the right support, you can work towards your weight loss goals while looking after your strength and long-term health.

Sources

• Body composition changes during weight reduction with tirzepatide in the SURMOUNT‐1 study of adults with obesity or overweight. (2025) Diabetes, Obesity and Metabolism. [Accessed 11 October 2026]
• Effect of resistance exercise on body composition, muscle strength and cardiometabolic health during dietary weight loss in people living with overweight or obesity: a systematic review and meta-analysis. (2025) BMJ Open Sport & Exercise Medicine. [Accessed 11 October 2026]
• Effects of Creatine Supplementation and Resistance Training on Muscle Strength Gains in Adults Under 50 Years of Age: A Systematic Review and Meta-Analysis. (2024) Nutrients. [Accessed 11 October 2026]
• Mounjaro. (2026) EMA. [Accessed 11 October 2026]
• Mounjaro – Product information. (2026) EMA. [Accessed 11 October 2026]
• Protein. (n.d.) British Dietetic Association. [Accessed 11 October 2026]
• Getting active for your lifestyle. (2023) HSE. [Accessed 11 October 2026]
• Delayed onset muscle soreness (DOMS). (2019) Dublin Sports Injury Clinic. [Accessed 11 October 2026]