What GLP-1 Medications Are Actually Doing Inside Your Body

Recently, I spent a full weekend at a practitioner symposium dedicated entirely to GLP-1 medications — the class of drugs behind Ozempic, Wegovy and Mounjaro — and the wider science of appetite, metabolism and weight regulation.

I came home with pages of notes and a much deeper appreciation for how complex this space really is. I'm seeing more and more clients using these medications, so I wanted to share what I learned in a way that's actually useful — not another "natural Ozempic" headline, and not a scare campaign either. Just what's genuinely happening in your body, explained simply.

This is Part 1 of a three-part series. Here I'm covering what GLP-1 medications are actually doing inside the body. In Part 2, I'll cover how to protect your muscle, bone and metabolism while you lose weight. In Part 3, I'll look at the natural pathways your own body already uses, and how naturopathic medicine may support them.

Obesity isn't a willpower problem

One thing I appreciated about the weekend was hearing obesity discussed as what it actually is: a complex, chronic metabolic condition — not a character flaw.

Genetics are estimated to account for somewhere between 40 and 80% of a person's risk of obesity. On top of that, hormones, sleep, stress, certain medications and simply living in a world full of convenient, highly processed food all play a role.

Your appetite isn't governed by willpower alone. It's regulated by a genuinely complex communication network between your gut, brain, pancreas and other organs.

Where GLP-1 fits in

GLP-1 (glucagon-like peptide-1) is a hormone your body already makes every time you eat. It helps regulate insulin and glucagon, slows down how quickly your stomach empties, and contributes to that "I'm full" signal.

GLP-1 medications work by mimicking this natural hormone — but with a much stronger, longer-lasting effect than the GLP-1 your body produces on its own. Native GLP-1 is broken down within 1–2 minutes by an enzyme called DPP-4. Semaglutide, by comparison, is engineered to last roughly a week. That difference is the entire reason the medication works so much more powerfully than your own biology.

Your body has a "set point" — and it fights to defend it

This was one of the most useful concepts from the weekend, because it explains something so many people have said to me in clinic:

"I can lose the weight. My body just seems determined to put it back on."

We have a biological drive to defend a certain weight range, and it's more sophisticated than most people realise. Your fat tissue communicates how much energy you have "in the bank" via a hormone called leptin — think of it as one internal scale. Fascinatingly, newer research suggests your bones may act as a second, independent scale, sensing the load your skeleton is carrying. Both feed into a control centre in your brain that's constantly weighing up your intake, your reserves and your energy needs — and quietly adjusting your appetite and metabolism to defend a familiar range.

This is exactly the same system I talked about in my earlier blog on why eating too little can stall your weight loss. When you eat too little for too long, your body reads it as a threat to its energy reserves and fights back — appetite goes up, resting metabolic rate (your BMR) goes down, and the scale stops moving even though you're "doing everything right." It's the same defence mechanism, just triggered from the restriction side rather than the medication side.

GLP-1 medications work from the other direction — they quieten appetite powerfully while you're taking them, which is exactly why they can feel so different to a typical diet. But quietening appetite isn't the same as switching off the underlying drive to defend your set point. That biology is still there, which leads to the question I think matters most.

What happens when you stop?

Data presented at the symposium showed that significant weight regain is common after stopping GLP-1 medications, with some research reporting around 60% of lost weight regained within a year — alongside some reversal of the blood sugar and blood pressure improvements gained along the way.

This is exactly why I don't think of these medications as a simple start-and-stop plan. There needs to be a genuine "off-ramp" — with nutrition, muscle and habits addressed well before the medication is withdrawn, not after.

Here's the encouraging part, though: biology isn't destiny. The National Weight Control Registry has tracked over 10,000 adults who lost significant weight and kept it off for 5+ years, and the pattern among them is remarkably consistent — regular activity (most exercise around an hour most days, largely just walking), a consistent way of eating rather than a weekday/weekend split, and catching small regains early through regular weigh-ins. The researchers behind it put it simply: effort offsets biology. Your set point isn't fixed forever — it responds to sustained habits, which is exactly what Part 2 of this series is about.

Side effects and other things worth knowing

Common side effects include nausea, reflux, a sense of excessive fullness, constipation and bloating — which make more sense once you understand that these medications slow gastric emptying while also reducing appetite.

Researchers are also exploring whether GLP-1 medications have applications well beyond weight loss. Areas being studied include heart failure, fatty liver disease, sleep apnoea and osteoarthritis, alongside early research into reward-seeking behaviours around alcohol and other substances. It's a great example of just how interconnected our metabolic, cardiovascular and brain chemistry really are — though most of this is still emerging research rather than settled treatment.

And if you're taking a GLP-1 and considering pregnancy, this is an important conversation to have directly with your prescribing doctor about appropriate timing.

Why I'm sharing this

If you're currently taking a GLP-1 medication, or considering one, my goal isn't to talk you into or out of it. These medications can be genuinely effective tools for the right person.

What I want you to know is that weight loss is only one part of the picture. How we protect your nutrition, muscle, bone and metabolic health along the way matters just as much — and that's exactly what Part 2 of this series covers.

Frequently asked questions

What does GLP-1 actually stand for?
GLP-1 stands for glucagon-like peptide-1, a hormone your body naturally produces in the gut every time you eat. It helps regulate blood sugar, slows gastric emptying and contributes to feelings of fullness.

Do you regain weight after stopping Ozempic or Wegovy?
Research presented at the symposium I attended found that significant weight regain — around 60% of lost weight within a year — is common after stopping GLP-1 medications, particularly without a planned nutrition, muscle and habit-focused "off-ramp."

Is weight regain inevitable?
No. Long-term data on people who successfully maintain weight loss (the National Weight Control Registry) shows that consistent activity, regular eating patterns and early course-correction significantly improve long-term outcomes, regardless of how the initial weight loss happened.

What's next

In Part 2, I'll cover the takeaway that hit me hardest over the whole weekend: rapid weight loss doesn't only come from body fat, and protecting your muscle and bone while using a GLP-1 medication takes deliberate support.

If you're currently using a GLP-1 medication or thinking about it, and you'd like support with the nutrition, muscle and metabolic side of things alongside your prescribing doctor, I'd love to see you in clinic — you're welcome to book a consult any time.