Introduction
GLP-1 medicines such as Wegovy (semaglutide) and Mounjaro (tirzepatide) are effective for weight loss and improving blood sugar control.
For most people, they are safe and well tolerated. However, a small number of patients may develop gallstones or gallbladder inflammation (cholecystitis), especially during rapid weight loss.
Understanding why this happens, and what symptoms to look out for, helps keep your treatment safe and effective.
What Are Gallstones?
The gallbladder is a small pouch under your liver that stores bile, a fluid that helps digest fats. Gallstones form when the components of bile (such as cholesterol) harden and clump together.
They can range in size from tiny grains to larger stones and may sometimes block bile flow, causing pain or infection.
How GLP-1 Medicines Are Linked
GLP-1 treatments themselves do not directly cause gallstones, but they can increase the risk indirectly through rapid weight loss.
When weight is lost quickly, the liver releases more cholesterol into bile, and the gallbladder empties less often, both of which make stone formation more likely (1-3).
This can occur with any rapid weight-loss method, not just medication. In studies, gallbladder-related events were reported in about 1-2% of people using semaglutide or tirzepatide. Most cases were mild and treatable, but being aware of symptoms is important so they can be managed early.
Who May Be at Higher Risk
Your chance of developing gallstones may be slightly higher if you:
- Lose weight very quickly (over 1–2 kg per week).
- Have a history (or family history) of gallstones
- Are female
- Eat a very low-fat diet or skip meals regularly.
Symptoms to Watch For
Speak to your doctor or pharmacist if you notice any of the following:
- Pain in the upper right abdomen (especially after fatty meals).
- Pain under the ribs or radiating to the shoulder or back.
- Nausea or vomiting that doesn’t settle.
- Yellowing of the skin or eyes (jaundice).
- Fever, chills, pale stools, or dark urine.
If the pain is severe or constant, or if you have fever and vomiting, call 999 or go to A&E, as this may indicate acute gallbladder inflammation or bile duct blockage.
How to Reduce Your Risk
- Aim for gradual, steady weight loss (around 0.5–1 kg per week is ideal).
- Eat regular, balanced meals rather than skipping food.
- Include some healthy fats such as olive oil, avocado, or nuts as this helps the gallbladder empty.
- Stay hydrated throughout the day.
Summary
Gallstones are a rare but possible side effect during rapid weight loss with GLP-1 medicines.
The risk is small and can be reduced by losing weight gradually, eating regularly, and staying hydrated.
If you notice upper abdominal pain, nausea, or yellowing of the eyes or skin, contact your doctor promptly.
With early recognition and management, most people can continue their treatment safely.
References
- Nauck MA, Meier JJ. Effects of GLP-1 receptor agonists on the hepatobiliary system. Diabetes Obes Metab. 2022;24(10):2029–40.
- Wadden TA, Bailey TS, Billings LK, et al. Effect of semaglutide 2.4 mg on gallbladder-related events in the STEP trials. Obesity (Silver Spring). 2023;31(7):1685–96.
- Frias JP, Nauck MA, Van J, et al. Efficacy and safety of tirzepatide versus semaglutide once weekly in type 2 diabetes (SURPASS-2). N Engl J Med. 2021;385(6):503–15.