What is a GLP-1 and how does it help with weight loss?

What does GLP-1 stand for?

GLP-1 stands for glucagon-like peptide-1. It's a hormone produced in your gut after you eat. Its job is to signal to your brain that you've had enough food, slow the rate at which your stomach empties, and trigger insulin release to help manage blood sugar.

In people with obesity, this signalling system can be less responsive — meaning hunger doesn't switch off as reliably. GLP-1 medications work by amplifying or mimicking this signal.

How do GLP-1 medications cause weight loss?

The main effects are:

• Reduced appetite — you feel less hungry between meals and feel full sooner when eating
• Slower gastric emptying — food stays in your stomach longer, extending the feeling of fullness
• Reduced food cravings — some patients report fewer cravings for high-calorie foods, though the mechanism is still being studied

The result is that most people naturally eat less — not by willpower, but because the biological signals that drive hunger are reduced.

How effective are they?

Clinical trials have shown significant results. In trials for Wegovy (semaglutide 2.4mg), participants lost an average of around 15% of their body weight over 68 weeks alongside lifestyle support. Mounjaro (tirzepatide) has shown even higher average weight loss in trials — up to around 20–22% in some studies.

These are averages. Individual results vary, and medication works best alongside dietary changes and physical activity — not as a replacement for them.

What are the common side effects?

The most frequently reported side effects are gastrointestinal — nausea, vomiting, diarrhoea, and constipation — particularly when starting or increasing the dose. These tend to improve over time. Doses are increased gradually for this reason.

More serious side effects are rare but include pancreatitis and gallbladder issues. Your prescribing team will discuss your individual risk profile.

What happens when you stop taking them?

This is an important question. Weight regain after stopping GLP-1 medication is common — studies suggest a significant portion of weight lost may return within a year of stopping. This is why programmes like Oviva combine medication with longer-term lifestyle support, to help build habits that last beyond the medication itself.

Are GLP-1 medications safe long-term?

Semaglutide (Ozempic/Wegovy) has been used in clinical practice for over a decade for type 2 diabetes, with a well-established safety profile. Long-term data specifically for the higher weight-loss doses is more recent but continues to be studied. As with all medications, the benefits need to be weighed against individual risks — something your pharmacist or GP can help with.