Bimagrumab: How this drug could help with weight loss and muscle gain

Bimagrumab is a medication currently being tested to help people lose body fat while keeping or gaining muscle. It was first developed by Novartis and is now being studied by Eli Lilly. It is not licensed or approved anywhere yet, and you cannot buy it in the UK.

Bimagrumab is a ‘monoclonal antibody’, which means it’s a type of protein made in a lab to target specific cells in the body. In clinical studies so far, it has been given as an infusion into a vein every 4 weeks, rather than a self-injection like Wegovy or Mounjaro.

Researchers are still running trials to check how well it works, how safe it is, and whether it could become a future treatment for weight loss and muscle gain.

Bimagrumab helps the body build more muscle while breaking down extra body fat. It does this by blocking a signal that normally tells your muscles to stop growing. When that signal is turned off, the body can change its balance of muscle and fat.

Because of these effects, people in early studies lost fat while gaining a small amount of muscle. However, research is still ongoing, and scientists are still testing bimagrumab to understand how well it works and who it might help in the future.

Current research on bimagrumab includes a 48-week clinical trial testing how well bimagrumab helps people to lose fat and gain muscle. The study included 75 adults who were overweight or obese and had type 2 diabetes. Some people were given bimagrumab, while others had a placebo. Everyone also received advice about healthy eating and staying active.

Trial overview

The main results come from a phase 2 study. People in the trial received bimagrumab as an infusion into a vein every 4 weeks for 48 weeks. The placebo group followed the same schedule.

Average changes in body weight and body fat

After 48 weeks, people taking bimagrumab had:

• around 20% less body fat, compared with almost no change in the placebo group
• about 3 to 4% more lean muscle, while the placebo group lost a small amount
• around 6 to 7% total body weight loss, compared with less than 1% in the placebo group
• a drop of about 9cm in waist size, while the placebo group saw no meaningful change

How effective is bimagrumab?

Existing trials show that bimagrumab is very effective at reducing body fat and increasing muscle at the same time. This makes it different from many weight loss medications, which can cause some muscle loss as the body gets lighter.

However, the total weight loss seen in the study (around 6 to 7%) was lower than what is usually seen with GLP-1 treatments such as Wegovy, Mounjaro and Ozempic. This is one reason why researchers are now studying bimagrumab on its own and together with semaglutide to see whether the combination can lead to greater overall results.

More studies around bimagrumab are still needed to get a true and safe overall picture of the effectiveness.

Bimagrumab is still being studied, so we only have early information about its side effects.

Most people in trials had mild or moderate symptoms, while a smaller number had more serious reactions. As research continues, we will learn more about how safe it is. For now, here is an overview of current findings:

Common side effects

In clinical trials, the most common side effects included:

• diarrhoea
• muscle spasms
• colds or other mild breathing infections
• skin reactions such as a rash
• nausea

These side effects were usually short-lived and tended to happen early in treatment.

Serious side effects to be aware of

A small number of people had more serious reactions, including:

• pancreatitis
• pneumonia
• raised liver enzymes on blood tests

Some people also stopped treatment because of side effects.

Some of these serious reactions may be caused by taking the medication or may have happened while the person was going through the clinical trial and may be unrelated. More research is needed to check this, so that a list of side effects can be confirmed.

These reactions were uncommon, but they show why close medical supervision will be important if bimagrumab becomes available in the future.

Bimagrumab is not available to buy in the UK, and there is no confirmed approval date. It is still being tested in clinical trials, and one planned obesity study has already been stopped. Even if results are positive, it would likely take several years before it’s approved.

Current trial status

Right now, bimagrumab is still in phase 2 trials for people who are overweight or obese. Research includes:

• an ongoing study which tests bimagrumab on its own and together with semaglutide in adults with obesity – results are expected in 2026
• a phase 2b trial planned for people with obesity and type 2 diabetes (using bimagrumab alone and with tirzepatide) – is currently cancelled for “strategic business reasons”

Regulatory approval timeline

For a new weight loss drug to be approved in the UK, manufacturers usually need:

• successful phase 3 trials in large groups of patients
• full safety data over a long period
• review and approval from regulators such as the Medicines and Healthcare products Regulatory Agency (MHRA)

Bimagrumab has not yet reached phase 3 for obesity. Because one planned trial has been stopped and the focus has shifted to combination treatment with semaglutide, the development path is less clear than for other weight loss medications.

Expected availability

Since bimagrumab is still in mid-stage research and has no phase 3 obesity results, it’s unlikely to become available in the UK within the next few years. Any timeline would depend on:

• whether ongoing trials show clear benefits on top of semaglutide
• whether the company decides to move into large phase 3 studies
• how regulators view its benefits compared with risks

Until those steps happen, bimagrumab will remain an experimental drug only available in clinical trials. Other new treatments, such as orforglipron, are also being developed for weight loss and may be available sooner.

Bimagrumab does not have an approved dosing plan for weight loss yet. At the moment, it‘s only used in research studies, where doctors decide the dose and give the treatment in a controlled setting. You cannot use it at home, and no official dose has been confirmed.

How bimagrumab was taken in studies

In earlier trials, bimagrumab was given as an infusion into a vein:

• once every 4 weeks
• in a controlled environment such as a clinic or hospital
• and used for up to 48 weeks (in the main phase 2 obesity trial)

Each dose was based on body weight, and people were monitored during the infusion.

Newer research into subcutaneous dosing

More recent studies suggest that a subcutaneous (under-the-skin) form of bimagrumab, the same way that you can take weight loss injections like Wegovy, may work as well as intravenous (administered into a vein through an IV drip) dosing.

This means that in the future, bimagrumab could be developed as a weight loss injection rather than a drip.

However, currently:

• no approved injection pen or home-use version exists
• the exact dose, timing, and strength have not been set
• any future schedule will only be confirmed once larger trials are completed

So far, research has not included a step-by-step dose increase (dose escalation), but this could change if a self-injection version is created.

Administration technique

Because bimagrumab is still in trials, all doses are given by trained healthcare staff. In studies, this means:

• the medicine is prepared in a clinical setting
• a small tube is placed into a vein in the arm
• the infusion is given slowly over a set time
• people stay in the clinic so staff can check for side effects

If the subcutaneous version moves forward, it may eventually become a simple injection under the skin. For now, this remains experimental and is not available for general use.

Bimagrumab is not approved yet, so there are no final rules about who can use it. Early studies included adults with overweight or obesity, so future criteria will likely be similar to other private weight loss treatments.

Eligibility criteria (if approved)

We do not know for sure yet what the eligibility criteria will be. In the phase 2 trial, the BMI of study participants was 28 or more with a health-related condition, but more trials will be carried out to check the suitability for other patient groups before eligibility is confirmed.

Who should not use it

Bimagrumab may not be suitable for people who:

• are pregnant or breastfeeding
• have pancreatitis or a history of pancreatitis
• have serious liver, stomach, or bowel problems
• have allergies to similar medicines

Final safety guidance will only be available once more research is completed.

The price of bimagrumab has not been confirmed yet, as it’s still being studied and has not been approved for use. When it does become available, the cost may be similar to other private weight loss injections. For example:

• Wegovy usually costs £99 to £200 per month depending on the dose
• Mounjaro can cost £150 to £300 per month depending on the dose

Because bimagrumab is a more complex treatment that targets both fat and muscle, it may fall at the higher end of this range. Exact pricing will only be known if the treatment is approved and launched in the UK.

Bimagrumab works in a different way from medications like Wegovy, Mounjaro and liraglutide. Those treatments mainly help you feel less hungry, while bimagrumab aims to lower body fat and help keep your muscle at the same time. This makes it a different kind of weight loss medication, but it is still being tested and not available yet.

Bimagrumab vs Wegovy (semaglutide)

Bimagrumab and Wegovy work in different ways and are at very different stages of approval.

Bimagrumab vs Mounjaro (tirzepatide)

Bimagrumab and Mounjaro work through completely different hormone pathways and have different effects on muscle.

➤ You can see how current treatments compare in our guide on Wegovy vs Mounjaro vs Ozempic.