Why Do GLP-1 Injections Cause Muscle Loss in Midlife Women (And What Happens When You Come Off Them)?

GLP-1 injections like Wegovy, Ozempic and Mounjaro cause muscle loss because they take the weight off fast, and when weight comes off fast, a big chunk of it is muscle, not just fat. In the main semaglutide trial, close to half the weight people lost came from lean tissue, which includes muscle. For women over 40, who are already losing muscle to perimenopause, that is a real problem.

And here is the part nobody tells you. Most women come off these drugs within a year or two. When they do, the weight comes back. But it comes back as fat, not muscle. So you can end up lighter on the scales at your lowest point, then heavier in body fat than when you started, with less muscle to hold it all together. That is the bit that matters, and it is why the injection alone is rarely the full answer.

I am 55. I lost 5 stone in perimenopause, and I did not do it with a needle. I am not here to scare you off medication or tell you what to inject, that is a conversation for you and your doctor. I am here to tell you what the research actually shows about muscle, so you can protect yours whatever you decide.

The quick version

• In the main semaglutide trial, about 40 to 45% of the weight lost came from lean tissue, including muscle.
• Women and older women in particular seem to be at higher risk of losing muscle on these drugs.
• When people stop, they regain around two thirds of the weight within a year, and it returns mostly as fat.
• Muscle you lose in your 50s does not just come back on its own. You have to build it back.
• Strength training and enough protein can cut the muscle loss to almost nothing, on the drug or off it.

What the injections actually do to muscle

These drugs work by dulling your appetite. You eat a lot less, so you lose weight. That part works, and for some women it is genuinely helpful.

But your body does not only burn fat when you eat less. It burns muscle too. The faster the weight comes off, and the less protein and strength work you are doing, the more of that loss is muscle.

The numbers are clear. In the STEP-1 trial of semaglutide, published in the journal Diabetes, Obesity and Metabolism, 45.2% of the weight people lost came from lean mass. In the SURMOUNT-1 trial of tirzepatide, the drug in Mounjaro, it was 25.7%. So somewhere between a quarter and nearly half of the loss was not fat at all.

The SEMALEAN study in 2025 followed 106 people, most of them women, and found lean mass dropped in the first 7 months before it settled. And a review shared by the Endocrine Society in 2025 flagged that women and older adults may be more at risk of muscle loss on these drugs, and that eating more protein helps protect against it.

Why this hits women over 40 harder

Here is what makes it worse for us. You are already losing muscle.

From your 40s onwards, muscle starts to slip away on its own. It is a normal part of ageing, and perimenopause speeds it up as oestrogen drops. The proper name for it is sarcopenia. You do not feel it happening. You just notice you are softer, weaker, more tired, and the lid on the jar is suddenly harder to open.

Now add a drug that pulls off another slice of muscle on top. You have two forces working against the same tissue at the same time. For a woman in her 50s, that is the difference between staying strong and independent, and feeling frail sooner than she should.

Muscle is not about looking toned. It is your engine. It burns energy all day, it holds your blood sugar steady, it keeps your bones strong, and it is what lets you carry the shopping and get up off the floor at 70. Losing it is the last thing a midlife woman needs.

What happens when you stop the injection

This is the part I most want you to understand.

These drugs are not designed to be a quick fix you do for a few months. They work while you take them. Most people, though, do come off them, whether that is cost, side effects, supply, or just wanting their life back.

And when they stop, the weight returns. The STEP-1 extension study followed people after they came off semaglutide. Within a year, they had regained about two thirds of the weight they had lost. Their blood pressure and blood sugar drifted back towards where they started too.

Now think about what that regained weight is made of. When weight comes back after a diet or a drug, it comes back as fat first. Muscle only rebuilds if you train for it. So the woman coming off the injection can end up with more fat and less muscle than she had at the very beginning. Lighter for a while, then worse off underneath.

That is the leaky bucket. You can keep pouring effort, or money, into the top. But if the bucket is leaking muscle out the bottom, you never get to keep what you gained.

How to protect your muscle, on the drug or off it

The good news is that muscle loss is not a given. It is largely preventable, and the fix is not complicated.

The research is consistent on this. When people lifting weights and eating enough protein lose weight, they hold on to almost all their muscle. The loss drops close to zero. It works whether you are on a GLP-1 or not.

Here is what that looks like in real life, without turning your week upside down.

Lift something heavy, a few times a week. You do not need a gym or hours you do not have. Two or three short strength sessions a week is enough to tell your body to keep its muscle. This is the single most important thing, on the drug or off it.

Eat more protein than you think you need. Most women over 40 eat far too little. Aim to get a good source of protein into every meal, starting with breakfast. This gives your muscle the material to hold on and rebuild.

Go a little slower. Losing weight at a gentler pace protects more muscle than crash losing. If you are on a drug, that is worth raising with your doctor.

Think past the injection. If you do use one, treat it as a window to build the strength and habits that keep the result once you stop. The drug can lower the appetite. Only you can build the muscle.

None of this is about doing more, harder. It is about doing the one thing that actually holds the result together, instead of pouring everything into a bucket that leaks.

Common questions

Do GLP-1 injections cause muscle loss in everyone?
Not to the same degree. How much muscle you lose depends heavily on how fast you lose weight, how much protein you eat, and whether you are doing any strength training. People who lift and eat enough protein lose very little muscle. People who just take the drug and eat less lose the most. So a lot of it is in your hands.

I am over 50. Is it too late to build muscle back?
No. Women in their 50s, 60s and beyond build muscle when they train for it. Your body still responds. It may be a little slower than at 30, but the ability does not switch off. I started rebuilding mine at 55 and I am stronger now than I was at 40.

Should I stop taking my GLP-1 medication?
That is not my call to make, and please do not stop or change any medication based on a blog. That is a decision for you and your doctor, who know your full history. My job is to help you protect your muscle and build your strength whatever you and your doctor decide about the drug.

Will eating more protein make me gain weight?
Protein is the nutrient most likely to keep you full and least likely to be stored as fat. For most women over 40 the issue is eating too little protein, not too much. Getting enough is one of the most useful changes you can make for energy, appetite and muscle.

What is Body Reclaim and who is it for?
Body Reclaim is my program for women in perimenopause and beyond who are tired of plans that were never built for their changed body. It is built on one little change a week, starting with energy and strength, using the Compound Method. It is for the woman who has tried everything and wants something that actually holds. Join the waitlist to be notified when the next intake opens.

The thing worth remembering

The injection is a tool. It can quiet the appetite and take weight off. What it cannot do is build the muscle that keeps you strong, steady and independent as you age. Only strength work and enough food can do that.

So whatever you decide about medication, protect your muscle. It is the one thing that holds the whole result together, and the one thing that does not come back on its own.

Join the waitlist to be notified when the next Body Reclaim enrolment opens.

Jane Cox is a fitness coach for women in perimenopause and menopause. She lost 5 stone in perimenopause at 55 and built Body Reclaim to help women get their strength and energy back with one little change a week. She is not a doctor, and nothing here is medical advice. Always speak to a qualified professional about medication and your own health.