How GLP-1 Drugs Work

GLP-1 stands for glucagon-like peptide-1, a hormone released from the gut after eating. Medicines like semaglutide, liraglutide, and tirzepatide imitate this hormone’s effects.

They slow how quickly food leaves the stomach, signal fullness to the brain, and stabilise blood sugar by improving insulin release and lowering glucagon.

This combination reduces calorie intake and supports gradual, sustainable weight loss.

Your gut and brain communicate constantly about hunger and fullness. GLP-1 drugs strengthen the body’s natural “I’m full” signals.

• The gut releases your own GLP-1 after meals.
• This hormone travels through the bloodstream and activates receptors in the brain’s appetite centre (the hypothalamus).
• Enhancing this hormone with medication means feel satisfied sooner and stay full longer.
• Over time, this helps you eat less without intense hunger.

GLP-1 drugs slow how quickly food leaves the stomach, helping you feel full between meals and reducing post-meal blood sugar dips and peaks. This slower emptying means:

• Smaller meals feel more satisfying.
  
• Blood sugar rises more gradually after eating.
• The pancreas has more time to respond with insulin.

These effects are strongest when starting treatment and settle into a steady rhythm over time.

GLP-1 drugs help your pancreas release insulin when it’s needed, lowering blood sugar effectively.

• Boosts insulin release when glucose levels rise.
• Reduces glucagon (a hormone that raises blood sugar).
• Helps stabilise day-to-day glucose levels even in people without diabetes.

GLP-1 drugs reduce cravings by changing how the brain responds to food cues and rewards.

• People often report fewer cravings for high-calorie foods.
• The drugs affect dopamine-linked reward circuits, making food feel less tempting.
• This helps break the cycle of emotional or habitual eating.

GLP-1 drugs influence many systems beyond appetite: improving blood pressure, cholesterol, and even inflammation.

• Lowers systolic blood pressure.
• Improves lipid profile and decreases atherosclerosis in blood vessels.
• Reduces inflammation and oxidative stress.
• May benefit liver fat and sleep-apnoea severity as weight decreases.

Some new medicines, like tirzepatide (Mounjaro), activate both GLP-1 and another hormone called GIP, producing even greater effects on weight and metabolism.

• GIP (glucose-dependent insulinotropic polypeptide) enhances insulin sensitivity and fat metabolism.
• When combined with GLP-1 action, it creates a synergistic response leading to more significant weight and glucose improvements.
• This dual approach can achieve up to 20–22 % average weight loss in trials.

If you stop taking the medicine, hunger usually returns and some weight may come back. Maintaining healthy habits makes it easier to keep the progress you have gained.

GLP-1 therapy doesn’t permanently change hormone levels; appetite and digestion return to baseline over time. Lifestyle habits learned during treatment help prevent regain.

Dr Abby Hyams completed her medical training in Bristol and has been a GP for 19 years, spending many of those as a partner in an NHS practice in Hemel Hempstead. She has a particular passion for supporting patients with weight loss and promoting positive behaviour change, helping individuals build sustainable habits that improve their long-term health and wellbeing.

• Wilding JPH et al. NEJM 2021 (STEP 1)
• Jastreboff AM et al. NEJM 2022 (SURMOUNT-1)
• Pi-Sunyer X et al. NEJM 2015 (SCALE)
• Marso SP et al. NEJM 2016 (SUSTAIN-6)
• van Bloemendaal L et al. Diabetes 2014
• NICE NG248 (2023); TA875 (2023)
• EMA EPARs for Wegovy, Mounjaro, Saxenda

This article is for general information only and should not be used for the diagnosis or treatment of medical conditions. Medic Spot Limited has used all reasonable care in compiling the information but makes no warranty as to its accuracy. Consult a doctor or other healthcare professional for diagnosis and treatment of medical conditions. In the event of an emergency, please call 999 for immediate assistance.

There is no guarantee of a specific weight loss medication being prescribed. Clinicians will review your online questionnaire alongside other independently validated medical information about you and will recommend the most appropriate weight loss treatments for you based on your answers. In some cases, the clinicians may contact you for additional information. See Terms of Service for more information.