The Gap I See in People Taking GLP-1s

Before you read this, know this: I think GLP-1s can be the right call for the right person. This isn't an anti-medication post. But more often now, someone tells me they just started one, and I ask the same question back. Has anyone explained to you the lifestyle changes that should go along with it?

Usually, the answer is no (not always, there are some amazing providers out there who cover this). They got a prescription, a quick rundown of side effects, and sent on their way. Nobody talked to them about lifting, about diet changes, about what actually happens to their body while the weight comes off. That gap is what this post is about.

GLP-1 medications, semaglutide, tirzepatide, liraglutide, whatever brand name you have heard, Ozempic, Wegovy, Zepbound, Mounjaro, are everywhere right now. I am not here to tell you whether you should take one. That is between you and your doctor. What I can tell you is what I have learned about training people who do, and where the picture most people carry around in their head is wrong.

What These Medications Actually Do

GLP-1 stands for glucagon like peptide 1, a hormone your gut already makes after you eat. These drugs mimic it. They slow how fast food leaves your stomach, they help regulate insulin and blood sugar, and they turn down the volume on hunger signals in your brain. That is the mechanism. They were built for type 2 diabetes first, and the weight loss effect showed up as a very useful side effect, useful enough that most of the newer versions are now approved specifically for weight management.

You have probably heard the brand names more than the drug names. Semaglutide is Ozempic when it is prescribed for diabetes and Wegovy when it is prescribed for weight loss, same drug, different label. Tirzepatide shows up as Mounjaro or Zepbound the same way. Liraglutide, the oldest of the group, goes by Victoza or Saxenda. Different molecules, different dosing, but the same basic family and the same basic mechanism underneath.

None of that involves muscle. None of it involves strength. These are appetite and metabolism drugs, not fitness drugs.

What They Are Not

Here is the assumption I run into constantly: the number on the scale is going down, so the fat is what is leaving. That is not how weight loss works, with or without medication, and it is especially not how it works here. Karakasis and his colleagues pooled 22 randomized trials on these drugs and found that lean muscle mass made up roughly a quarter of the total weight lost, and that share got worse, not better, on the more powerful versions of the drug [1]. Tirzepatide and semaglutide at their strongest doses were among the worst performers for protecting lean mass. Liraglutide, the oldest and gentlest of the bunch, was the only one in that whole analysis that produced real weight loss without a significant lean mass hit.

So the honest answer to “are GLP-1s good or bad for muscle” is that it depends almost entirely on what else is happening around the medication. Left alone, with no training and no attention to protein, a real chunk of what comes off is going to be muscle. Nobody warns you about that part. It's exactly why training doesn't get scaled back once someone starts one of these drugs in my program. It gets turned up.

The Debate I Watch Play Out In The Research

There is an actual argument happening in the medical literature right now about whether this muscle loss even matters. Linge and his co-authors put it as a real open question in a recent Circulation review: is the muscle change from these drugs adaptive, meaning proportional and expected as the body gets smaller, or maladaptive, meaning it is compromising something people will feel later [2]. The honest answer from the researchers themselves is that we do not fully know yet, and that better imaging and better muscle quality measures are needed to sort it out.

I will tell you where I land as a coach, not as a researcher. I do not need a final verdict on adaptive versus maladaptive to know that showing up lighter but weaker is a bad trade for almost every person I work with, whether they are a competitive athlete or someone just trying to move well into their sixties. Function matters more than the number on the scale, every time.

Who This Matters Most For

Everyone taking one of these medications should be thinking about muscle, but a few groups need to be paying extra attention. Older adults are already losing muscle mass every year just from aging, and stacking a medication driven weight loss on top of that without a plan can push someone toward real frailty faster than they expect. And honestly, anyone who has fought hard to build muscle over the years should think twice before letting a medication quietly undo years of work in the gym.

This is not a reason to avoid these medications if you and your doctor have decided they make sense for you. It is a reason to walk in with a plan instead of finding out after the fact what got left behind.

How I Actually Program Around This

This is the part nobody tells people when they start one of these medications, so it is the part I lead with.

• Resistance training stays in the program. Non negotiable. Codella and colleagues looked specifically at exercise and GLP-1 use, and resistance training, not cardio, came out as the piece that actually protects lean mass during a medication driven weight loss [3]. Somebody starts one of these drugs, their lifting gets more of my attention, not less.

• Protein gets prioritized hard. Appetite suppression is the whole point of these medications, which means total food intake drops, and protein is usually the first thing to fall short when someone is eating less without thinking about it.

• I adjust expectations around energy and recovery. Reduced appetite plus lower calorie intake can mean less fuel going into a session. I watch for that and scale volume or intensity rather than pretending it is not happening.

• I track strength and function, not just the scale. If someone's weight is dropping but their numbers in the gym are dropping too, that is the signal to intervene, adjust programming, push protein, and loop in their prescriber if needed.

• I stay in my lane. The medication belongs to whoever prescribed it. I work alongside them, and if something concerning shows up in a session, that gets relayed to the prescriber. I don't play doctor.

None of this means the medications are bad. They're a legitimate medical tool, and they've genuinely helped a lot of people. My job is making sure the person across from me doesn't trade away their strength for a smaller number without realizing that was ever the deal.

Bottom Line

GLP-1 medications do one job well: they turn down appetite and help regulate blood sugar. They do not build muscle, they do not automatically protect it, and left unmanaged they can take a real bite out of it. My approach does not change because someone is on one of these drugs. I still prioritize resistance training, I still push protein, I just pay closer attention while I do it.

If you are on a GLP-1, or thinking about starting one, and nobody has talked to you about training around it, that is exactly the conversation I want to have.

Sources & Further Reading

1. Karakasis P, Patoulias D, Fragakis N, Mantzoros CS. Effect of glucagon like peptide 1 receptor agonists and co agonists on body composition: Systematic review and network meta analysis. Metabolism, 2025. https://www.sciencedirect.com/science/article/abs/pii/S002604952400341X

2. Linge J, Birkenfeld AL, Neeland IJ. Muscle Mass and Glucagon Like Peptide 1 Receptor Agonists: Adaptive or Maladaptive Response to Weight Loss? Circulation, 2024. https://pubmed.ncbi.nlm.nih.gov/39401279/

3. Codella R, Senesi P, Luzi L. GLP-1 agonists and exercise: the future of lifestyle prioritization. Frontiers in Clinical Diabetes and Healthcare, 2025. https://pmc.ncbi.nlm.nih.gov/articles/PMC12683586/

This article is for general educational purposes and is not a substitute for individualized medical advice. Talk with your prescribing physician about any medication decisions, and consult a qualified clinician before starting or changing a training program.