New Drug May Help Prevent Muscle Loss on Mounjaro, Early Study Suggests

A new experimental drug called apitegromab could help people taking Mounjaro preserve more muscle while losing weight, according to research published in Nature Medicine and reported by BBC News in June 2026.

The six-month study followed 102 adults taking Mounjaro. Participants who also received apitegromab retained significantly more lean muscle mass than those receiving a placebo treatment. Researchers found lean mass accounted for 14.6% of total weight loss in the apitegromab group, compared with 30.2% in the placebo group. The researchers estimated this represented around 1.9kg more muscle being preserved during the six-month trial.

For the millions of UK adults now using weight loss jabs such as Mounjaro, Wegovy and Ozempic, the findings highlight a growing area of concern. While losing fat is the goal, preserving muscle is increasingly being recognised as an important part of achieving healthy long-term weight loss.

What the Research Actually Found

According to the study published in Nature Medicine, participants taking Mounjaro alongside the experimental drug apitegromab retained significantly more lean muscle mass than those receiving a placebo treatment. Over the six-month trial, lean mass accounted for 14.6% of total weight loss in the apitegromab group, compared with 30.2% in the placebo group. Researchers estimate this equated to around 1.9kg more muscle being preserved.

Muscle loss during rapid weight loss is a well-documented concern. When the body sheds fat quickly, it can also break down muscle tissue for energy. This matters because muscle keeps your metabolism healthy, supports your joints, and helps you stay independent and strong as you age.

According to Dr Marie Spreckley of Cambridge University, the findings represent encouraging early evidence. However, she was clear that larger studies are needed before firm conclusions can be drawn. This is the honest, cautious language of good science — and it is worth taking seriously.

According to Dr Brendan Gabriel of the University of Aberdeen, the intervention may not suit everyone. He noted it could be particularly helpful for people who are losing muscle at a faster-than-average rate. This is an important nuance. Not every person on Mounjaro loses the same amount of muscle, and individual circumstances matter enormously.

Why Mounjaro Muscle Loss Matters So Much Right Now

Mounjaro — the brand name for tirzepatide — works by mimicking two gut hormones that regulate appetite and blood sugar. It is currently the most powerful weight loss jab available in the UK. According to the MHRA, it is licensed in the UK for both type 2 diabetes and weight management.

Because Mounjaro can produce rapid, significant weight loss, the question of body composition — meaning the balance of fat to muscle — has become a pressing concern. Losing fat is the goal. Losing muscle alongside it is not.

This research directly addresses one of the most common concerns people have before starting Mounjaro: how much muscle might be lost alongside fat. The findings suggest that preserving muscle could become an important focus of future obesity treatment, with researchers now exploring medicines specifically designed to protect lean mass during weight loss.

According to the researchers, apitegromab works by blocking myostatin, a protein involved in regulating muscle growth. The treatment is currently only available within clinical trials, but researchers are investigating whether future versions could be delivered using a self-injection pen similar to existing GLP-1 weight loss medications.

If you are considering Mounjaro or are already using it, our full Weight Loss Jabs Guide explains how each treatment works in plain English, with no jargon and no sales pressure.

What This Means For UK Patients

This research does not mean apitegromab will be available to patients any time soon. The treatment remains experimental and is currently only available through clinical trials. However, the findings highlight a growing concern among obesity specialists: how to help patients lose fat while preserving as much muscle as possible.

For people currently taking Mounjaro, Wegovy or Ozempic, the message remains largely unchanged. Strength training, regular physical activity and adequate protein intake are still considered the best available ways to support muscle health during weight loss.

What has changed is that researchers are now actively exploring medicines designed specifically to protect lean muscle mass. If future studies confirm the early results seen with apitegromab, muscle-preserving treatments could eventually become part of obesity care alongside weight loss medications.

If you are considering Mounjaro or are already using it, speak to your prescribing clinician about how to support your muscle health during treatment. Our UK Clinic Reviews section looks honestly at which providers offer the most comprehensive support beyond simply issuing a prescription.

Frequently Asked Questions

How much muscle do you lose on Mounjaro?

In the Nature Medicine study reported by BBC News, participants taking Mounjaro alongside a placebo lost around 30.2% of their total weight as lean mass. Those who also received the experimental drug apitegromab lost around 14.6%, suggesting substantially greater muscle preservation. Individual results will vary depending on age, diet, activity levels and overall health.

Can exercise really protect your muscles while on Mounjaro?

Experts generally recommend resistance exercise and adequate protein intake while taking Mounjaro to help support muscle health. In the study discussed in this article, researchers were investigating apitegromab, an experimental drug designed to preserve muscle mass during weight loss. Larger studies are still needed before any definitive conclusions can be drawn.

Is Mounjaro available on the NHS for weight loss in the UK?

According to the MHRA, Mounjaro is licensed in the UK for weight management. NHS access is currently limited to specialist weight management services and is not yet available through standard GP prescriptions for most patients. Many people access it through regulated private clinics.

How much protein should I eat while taking Mounjaro?

Protein remains important during weight loss because it helps support muscle maintenance. Many healthcare professionals recommend aiming for a good source of protein with every meal. Individual requirements vary depending on age, weight, activity levels and health conditions, so personalised advice from a clinician or registered dietitian is always recommended.

If you want to understand the broader landscape of weight loss treatments available in the UK right now, including newer options on the horizon, our Start Here guide is the best place to begin.

This article is for information purposes only and does not constitute medical advice. Always consult a qualified healthcare professional before starting any treatment.