GLP-1 medications: what they do, what they don’t, and who they’re for

She had lost thirty-one pounds, and she was not happy about it.

She had gotten the prescription online — a form, a photo, a card on file, and a box on her porch. It worked, in the sense that the number on the scale went down every week. But she was exhausted. She was cold all the time. She had stopped going to the gym around week six because the workouts felt pointless, and she could not have told you why. She came in because she was thirty-one pounds lighter and felt worse than when she started.

Her scan told the story in about ten minutes. Of the thirty-one pounds, a little under a third of what she’d lost was lean mass. She had not been losing weight so much as disassembling herself, and nobody had been watching.

I want to be careful here, because this is not an argument against these medications. It is an argument against using them blind.

What GLP-1s actually do

Your gut already makes a hormone called GLP-1. You release it when you eat, and it does several sensible things at once: it tells your pancreas to release insulin when your blood sugar rises, it slows how quickly your stomach empties, and it signals your brain that you have had enough. It is part of the machinery that is supposed to make you stop eating.

These medications are engineered versions of that signal — longer-lasting, and far stronger than what your body produces on its own. The newer ones act on a second gut hormone as well, which is part of why they outperform the earlier generation.

What patients feel is the appetite signal. The constant negotiation with food goes quiet. For someone who has spent decades being told they lack willpower, that silence is often the first evidence that the problem was never willpower. It was biology, and the biology was drowning them out.

But underneath the appetite effect, something more interesting happens: insulin sensitivity improves, and the metabolic environment shifts in a direction that makes fat loss possible in bodies where it had stopped being possible. In trials, average weight loss lands somewhere around 10 to 15 percent of body weight. That is a real number, and nothing we had before came close.

The thing they don’t do

Here is what no one mentions on the telehealth intake form: GLP-1 medications do not know what kind of weight to take.

Any substantial weight loss costs you some lean mass — that is true of every diet ever studied. But these drugs are potent, the loss is fast, and the appetite suppression is indiscriminate. Protein intake falls along with everything else. Resistance training tends to fall away because you feel flat. And so the fat comes off, and the muscle quietly goes with it.

Muscle is not cosmetic. It is where you dispose of glucose, it is a large part of what your metabolism burns at rest, and it is what keeps you strong and upright decades from now. Trading it away to move a number on a bathroom scale is one of the worst deals in medicine — and it is invisible, because the scale applauds the whole time.

Two people lose twenty-five pounds. One lost twenty-two pounds of fat and held her muscle. The other lost seventeen pounds of fat and eight pounds of lean mass. The scale reports the identical result. Their metabolisms are now on opposite trajectories.

This is precisely why we scan body composition instead of trusting the scale. A DEXA tells us fat mass, lean mass, and visceral fat separately — so when we see lean mass slipping, we adjust the protein, the training, and the dose while it is happening, not a year later when someone wonders why their metabolism feels broken.

Why we look before we prescribe

The other reason to slow down is that weight is a symptom, and symptoms have causes.

When a woman in her forties tells me her weight stopped responding to the things that always used to work, the cause is frequently hormonal — and I have written about why that transition gets missed. An underactive thyroid will do the same thing. So will fasting insulin that has been climbing for years while the fasting glucose stayed reassuringly “normal.” So will low ferritin or a B12 sitting at the very bottom of the range, both of which flatten your energy in a way that no medication fixes.

Prescribe a GLP-1 into that picture and you may well get weight loss. What you will not get is a person who feels well, because the actual driver was never addressed — it was just outweighed. This is the gap between normal and optimal showing up again: the labs that come back unremarkable while the patient is unmistakably not.

So before anyone starts, we look. Thyroid, a full hormone panel, fasting insulin, HbA1c, lipids, nutrient status. A DEXA baseline, so we know what we are starting with. And resting metabolic rate — what your body actually burns at rest, measured rather than estimated from a chart. Sometimes that workup says a GLP-1 is exactly right. Sometimes it says the thyroid was the problem all along. You cannot know which without looking.

Who they’re for

They are for people whose biology is genuinely working against them, and who want the medication done properly — as one part of a plan that also protects muscle, corrects the hormonal and metabolic drivers underneath, and follows up often enough to catch problems early.

They are not for everyone. They are not appropriate for every medical history, and candidacy is a real clinical question rather than a checkbox. And they are not a shortcut for someone who has not been evaluated, because a medication this powerful deserves to know what it is walking into.

The question I get most often is what happens when you stop. It is a fair question, and the honest answer is that some regain is common — that is well documented. But look at why. If the only thing that changed was appetite suppression, then when the suppression ends, you are returned to the same metabolism you started with, now with less muscle than before. If instead your hormones were corrected, your insulin sensitivity improved, your nutrient deficiencies repleted, and your lean mass protected the whole way through, you are tapering into a body that is genuinely different. That is the entire difference between a prescription and a plan.

The honest answer

These medications are the most effective tools we have ever had for a problem that has humiliated people for generations, and I am glad they exist. I prescribe them. But the way they are most often sold right now — a form, a photo, a box on your porch, no labs, no scan, no follow-up — takes something genuinely good and strips out everything that made it medicine.

A GLP-1 is not a plan. It is one instrument inside one, and it works best when someone is watching what it is actually doing to you.

If you are considering a GLP-1, or you are already on one and something feels off, that is worth looking at properly. You can read more about how we approach medical weight loss, or request a consultation here.

Dr. Rowena Chua is the founder of Meliora Integrative Medicine in Evanston, IL and is triple board-certified in Neurology, Integrative Medicine, and Obesity Medicine. A longtime Evanston physician, she specializes in hormonal, metabolic, and neurological health.