GLP-1 weight loss injections all work on the same core hormone pathway, even though the specific medications differ.
GLP-1 weight loss injections like Mounjaro, Wegovy and Ozempic all work on the same core hormone pathway. Here’s how it actually works.
If you’ve been researching weight loss injections, you’ve probably seen the term “GLP-1” everywhere. It’s the hormone pathway behind medications like Mounjaro, Wegovy, Ozempic and Zepbound. Here’s what’s actually happening in your body when you use one, in plain English.
What is GLP-1?
GLP-1 (glucagon-like peptide-1) is a hormone your gut naturally releases after you eat. It does three main jobs: it tells your pancreas to release insulin, it slows down how quickly food leaves your stomach, and it signals to your brain that you’re full. GLP-1 medications are designed to mimic this hormone at levels much higher than your body produces on its own.
How the injection reduces appetite
Once injected, the medication binds to GLP-1 receptors in the brain’s appetite centre, reducing hunger signals and food cravings. At the same time, it slows gastric emptying — the rate at which food moves from your stomach into your small intestine — so you feel fuller for longer after eating smaller portions.
Some newer medications, like Mounjaro and Zepbound, go a step further by also activating a second hormone pathway (GIP), which appears to enhance the appetite-reducing effect. This is one reason tirzepatide-based medications have shown particularly strong results in clinical trials.
What results look like
Results vary by medication, dose, and individual response, but clinical trials for these medications have shown average weight loss ranging from around 15% to over 20% of starting body weight over 12-18 months, when combined with diet and lifestyle changes. Weight loss is typically gradual: most people see the biggest changes in appetite within the first few weeks, with the medication’s effect building as the dose is titrated upward over 2-4 months.
Common side effects
Because these medications slow digestion, the most common side effects are gastrointestinal: nausea, mild constipation or diarrhoea, and occasional reflux, especially during the first few weeks or after a dose increase. Side effects are usually most noticeable early in treatment and tend to ease as your body adjusts. Eating smaller, lower-fat meals and staying hydrated can help.
Are they all the same?
No. Wegovy and Ozempic both use semaglutide, but at different doses and with different licensing (Ozempic was originally developed for type 2 diabetes). Mounjaro and Zepbound both use tirzepatide. Saxenda uses an older GLP-1 medicine, liraglutide, taken as a daily rather than weekly injection. See our full weight loss injections range to compare pricing and dosing.
Frequently Asked Questions
Do I need a prescription for GLP-1 injections?
Yes. All GLP-1 medications are prescription-only. Our clinical team reviews every order against your health information before treatment is approved — see our eligibility assessment process for details.
How long before I see results?
Most people notice reduced appetite within the first 1-2 weeks, with visible weight loss typically building over 8-12 weeks as the dose is increased.
What happens if I stop taking it?
Appetite-suppressing effects fade once the medication clears your system, and without ongoing lifestyle changes, some weight regain is common — which is why these treatments work best alongside a sustainable diet and activity plan.
Can I take a GLP-1 injection if I don’t have diabetes?
Yes, medications like Wegovy, Mounjaro and Zepbound are licensed specifically for weight management in people without diabetes, subject to eligibility criteria such as BMI.
This article is for general information and isn’t a substitute for individual medical advice. Start your free eligibility assessment to find out which treatment, if any, is right for you.
Choosing between GLP-1 weight loss injections
With several GLP-1 weight loss injections now available — including Ozempic, Wegovy, Saxenda and Mounjaro — the right choice depends on dosing frequency, your prior response to treatment, and your prescriber’s clinical assessment, rather than a single best option for everyone. A free eligibility assessment is the quickest way to find out which of these GLP-1 weight loss injections you’re likely to be prescribed.