What is GLP-1, and what does it have to do with weight?

Medicines like semaglutide and tirzepatide have been making headlines for their role in helping people manage their weight. Both work by mimicking a hormone your body already makes called GLP-1, short for glucagon-like peptide-1.

Until recently, most people had never heard of GLP-1 or understood its function in the body. But once you know what GLP-1 does, it becomes much easier to see how these medicines work and why this hormone is so important for appetite, metabolism, and overall health.

What is GLP-1?

GLP-1 is a hormone produced in your gut (1–2). Every time you eat, your body releases it into the bloodstream. Here it acts as a messenger between your digestive system, brain, and pancreas.

These three systems all play a part in regulating appetite:

• Your digestive system controls how efficiently you process food and how full you feel.
• Your brain interprets hunger signals and controls food cravings.
• Your pancreas controls blood sugar levels through hormones like insulin.

Communication between these three organs is necessary for your body to function at a whole system level, helping it rebalance after eating. GLP-1 is the messenger that makes this possible. Without it, hunger, digestion, and blood sugar would be much harder to regulate.

What does GLP-1 do in the body?

GLP-1 triggers three main changes in the body that complement each other to help manage energy levels and appetite (2):

1. It slows digestion: In the digestive system, GLP-1 signals to the stomach to empty more slowly after eating (called delayed gastric emptying). This helps you feel fuller for longer.
2. It reduces appetite: In the brain, GLP-1 sends “I’ve eaten enough” messages to the areas that control appetite. This helps to stop cravings, quieten “food noise”, and lower hunger.
3. It regulates blood sugar: In the pancreas, GLP-1 increases insulin and reduces glucagon, which stops your blood sugar levels from spiking after meals.

Together, these actions help the body find balance. You feel satisfied after meals, are less likely to overeat, and experience steadier blood sugar levels.

After being released, GLP-1 is quickly broken down by enzymes within minutes. This gives it enough time to exert its effects while preventing the system from overcorrecting. As the effects wear off, your appetite will slowly return, and your blood sugar levels will settle into equilibrium.

How is GLP-1 linked to weight management?

Because GLP-1 directly affects your appetite, it’s closely linked to body weight regulation.

When GLP-1 levels are low (or when your body doesn’t respond to the hormone as effectively as it should), you may feel hungry soon after eating or crave more food than your body actually needs for fuel. Over time, this can cause overeating and make it harder to maintain a healthy weight.

Researchers discovered that boosting GLP-1 activity can help rebalance this system, leading to steadier blood sugar, better appetite control, and, for many people, gradual weight loss. That discovery eventually led to the development of GLP-1-based medicines.

What are GLP-1 medicines?

GLP-1 medicines are prescription treatments used for type 2 diabetes and weight management (1, 4).

They work by mimicking the action of your natural GLP-1 hormone: they bind to the same receptors in the gut, brain, and pancreas, triggering the same signals that reduce appetite, slow digestion, and support blood sugar control.

One key difference between natural GLP-1 and medicines like semaglutide and tirzepatide is how long they stick around in the body. Natural GLP-1 is broken down within minutes after eating, whereas GLP-1 medicines last longer (1, 3). This helps your body settle into a new, lower “appetite set point.”

Importantly, you still feel hungry around mealtimes thanks to your natural GLP-1 release, but your overall appetite is reduced. This makes it easier to eat smaller portions, avoid snacking, and ignore cravings, helping you lose weight safely and sustainably over time.

GLP-1 is part of a bigger picture

GLP-1 plays a crucial role in regulating hunger, blood sugar, and metabolism. But it’s one of the many hormones that tightly keep our bodies in balance. Others include:

• Ghrelin (“I’m hungry”) from the stomach
• PYY and CCK (“I’m full”) from the intestines
• GIP, which works alongside GLP-1 to boost its effects
• Sex hormones, cortisol, thyroid hormones, and many others.

Looking at the bigger picture helps to explain why weight is complex and why GLP-1 isn’t a magic switch for weight loss. While GLP-1 medicines can make weight loss more achievable, they should be combined with healthy habits that support your body as a whole (4).

Understanding GLP-1 is a great first step

GLP-1 might sound complicated, but it’s simply one of your body’s tools for telling you when you’ve eaten enough. By helping you feel full, digest food more slowly, and balance blood sugar, it also plays a crucial role in managing your weight.

If you’re struggling with your weight, GLP-1 treatments might be a good route to consider. But they’re not right for everyone and always require clinic oversight. If you’d like to explore whether GLP-1s could be a good option, Oxford Online Pharmacy’s team of pharmacists are here to help.

References

1. Zheng Z, Zong Y, Ma Y, Tian Y, Pang Y, Zhang C, et al. Glucagon-like peptide-1 receptor: Mechanisms and Advances in Therapy. Signal Transduction and Targeted Therapy. 2024 Sep 18;9(1):1–29.
2. Holst JJ. Glucagon‐like peptide‐1: Are its roles as endogenous hormone and therapeutic wizard congruent? Journal of Internal Medicine. 2022 Jan 24;291(5):557–73.
3. Friedman JM. The discovery and development of GLP-1 based drugs that have revolutionized the treatment of obesity. Proceedings of the National Academy of Sciences. 2024 Sep 19;121(39).
4. GOV.UK. GLP-1 medicines for weight loss and diabetes: what you need to know [Internet]. GOV.UK. 2025.