Mounjaro and muscle loss: How to protect and rebuild your strength

Yes, because Mounjaro can cause rapid, significant weight loss it can lead to muscle loss. Mounjaro does not directly target muscle tissue, but other effects of the drug often result in the loss of lean muscle mass (your body weight minus fat, including muscle, bone, and organ weight).

Muscle loss on Mounjaro can be caused by:

• calorie deficit, which is when you’re eating less calories than your body is burning
• reduction of protein intake, stopping you from sustaining muscle
• rapid weight loss, from not following a balanced lifestyle alongside treatment
• reduced metabolic demand as a result of lowered appetite caused by Mounjaro

How much muscle loss on Mounjaro is typical?

A sub-study of SURMOUNT-1 found that tirzepatide, the active ingredient of Mounjaro, can lead to a 10.9% reduction in lean mass. The study found that overall weight loss from tirzepatide resulted in roughly 25% of total weight loss coming from lean mass and 75% from fat mass (the fat on your body).

Although this may seem like a lot, it is commonly suggested that when losing weight in a calorie deficit, around 25% of overall weight loss comes from lean mass and is not a side effect unique to Mounjaro.

Muscle loss can cause several physical symptoms as muscles become smaller, weaker, and less effective. If you are losing muscle, you may notice that you are feeling:

• tired, fatigued or that you have lower energy levels than before
• weaker, for example, when lifting items
• unbalanced, sometimes leading to falls
• soreness in your muscles

You may also notice physical changes in your appearance, you may see that you are less toned even if you are exercising just like before.

The main thing you can do to help prevent muscle loss during Mounjaro treatment is to combine regular strength exercises with a protein-rich diet.

Strength exercises

Strength exercises and resistance training make your muscles work harder than usual by using your body weight or working against resistance to increase muscle size, strength, and power. It’s recommended to do at least 2 sessions of muscle-strengthening exercises a week.

Muscle-strengthening exercises include:

• yoga
• weight lifting
• push-up, sit-ups, and squats
• walking uphill
• cycling
• dancing
• climbing stairs

You should aim to do activities that target all major muscle groups (legs, hips, back, chest, abdomen, shoulders, and arms) and ensure you are working the muscle to the point where you may need a short rest before continuing.

Muscle-strengthening exercises can also help to improve the appearance of loose skin that may occur from weight loss.

Diet

As your dose of Mounjaro increases, your appetite will decrease, but it is important to make sure you are still eating a nutrient-dense diet. Here is an overview of key nutrients you need to maintain your muscle mass.

Protein

To maintain muscle mass on Mounjaro, you should eat enough protein. It is recommended that you should eat 0.75 to 0.8g of protein per kg of your body weight at a minimum. However, if you are trying to build muscle mass, you should aim for 1.4 to 2g.

Foods that are high in protein include:

• eggs
• dairy products, such as cottage cheese, Greek yogurt, or hard cheeses
• meat and poultry, such as chicken or turkey breast, lean ground beef, or jerky
• fish, especially oily fish such as salmon
• quinoa
• soy products, such as tofu or tempeh
• hemp seeds

Vitamin D and nutrients

It has been found that vitamin D also plays an important role in muscle function, and people who are deficient in vitamin D often have weaker muscles. It is important to make sure you are getting the recommended 10 micrograms of vitamin D daily.

During winter months and darker months it is important to make sure you eat foods containing vitamin D to ensure you are getting enough.

Foods which contain vitamin D include:

• red meat
• eggs yolk
• oily fish, such as salmon, sardines, trout, herring, or mackerel
• fortified foods, such as some fat spreads and breakfast cereals
• liver (this should be avoided if you are pregnant)

Other important nutrients to help maintain muscle mass are:

• omega-3, found in fatty fish (salmon and sardines), and flaxseeds
• calcium, found in dairy products such as milk, yogurt, and cheese
• magnesium, found in seeds, nuts, legumes, soy, and leafy greens
• iron, found in red meat, lentils, chickpeas, seeds, and nuts

Yes, you can rebuild muscle that is lost when taking Mounjaro.

To rebuild muscle, you need to combine consistent resistance training with a high-protein diet. Even with a reduced appetite, it is important to avoid skipping meals to ensure you have the required nutrients to help rebuild muscle.

Yes, you can gain muscle while on Mounjaro.

However, it will require an intentional effort to counter the possible muscle loss. The best way to gain muscle is to do consistent resistance training combined with a protein-rich diet.

You should speak to a doctor if you are experiencing a significant, noticeable decline in your strength that is affecting your daily life. For example, if you are struggling with any of the following:

• carrying shopping, laundry, or other objects
• climbing stairs
• rising from a chair, sofa, or the floor
• balancing

If you are following a balanced diet and regular exercise alongside treatment, experiencing these symptoms could indicate that it’s time to stop or pause your Mounjaro treatment journey. Your doctor may suggest an alternative treatment to Mounjaro.

Does Mounjaro cause muscle weakness?

Yes, it can, although it is not a direct side effect, Mounjaro can cause muscle weakness as a result of rapid weight loss, significant calorie decrease, and reduction in protein intake.

Can Mounjaro cause muscle aches?

Yes, it is not a listed side effect of Mounjaro, but some people have reported muscle aches and pains when using Mounjaro.

Does Mounjaro burn muscle?

No, Mounjaro does not directly burn muscle, but muscle loss can be a result of rapid weight loss.

How much protein should I eat on Mounjaro?

It is recommended that people should eat around 0.75 to 0.8g of protein per kg of body weight a day in order to maintain muscle mass. If you are looking to increase muscle mass, then 1.4 to 2g per kg of body weight is recommended.

For more guidance, check out our tools and resources to help you find out more about:

➤ What to eat on Mounjaro from our in-house experts

➤ Calculating how much protein your body needs during treatment with our protein calculator.

Is it safe to exercise while taking Mounjaro?

Yes, it is safe to exercise while taking Mounjaro and is recommended to aid weight loss, maintain muscle mass, and improve overall health.

What happens to my muscles when I stop taking Mounjaro?

Stopping Mounjaro will not have a direct effect on your muscles. It is common to regain some weight after stopping Mounjaro, and most of the weight is from fat and not muscle, which can make you feel weaker.