Can Weight Loss Injections Cause Gallstones?

You've started injections, lost weight quickly, and now your side feels wrong

It tends to go like this: you've been on treatment for a few months, appetite has dropped, weight is coming off steadily, and then there's a new ache, upper right, perhaps moving toward your shoulder blade, perhaps with nausea. That combination deserves attention. Gallstones are one of the better-recognised complications of significant weight loss, and they can develop even in people who had no gallbladder problems before. The NHS patient information for tirzepatide lists gallbladder problems among the side effects that require medical review. The same goes for semaglutide. If you're experiencing that pattern of symptoms, contact your GP or call 111 rather than waiting for your next review. Do not try to manage gallbladder pain at home.

The connection between weight loss injections and gallstones isn't a fringe concern, it appears in the clinical trial data for both medicines and is listed in their Summaries of Product Characteristics. That doesn't mean everyone develops them; most people on treatment don't. It means it's a risk worth understanding before you start, particularly if you have other factors working against you.

Why rapid weight loss (not just the injection) is the main driver

The gallstone risk during GLP-1 treatment has two overlapping causes, and separating them matters. The first is the weight loss itself. When fat tissue breaks down quickly, the liver compensates by secreting more cholesterol into bile. Bile that is unusually rich in cholesterol is supersaturated, meaning crystals form more readily. This happens with any method of rapid weight loss: crash diets, bariatric surgery, and GLP-1 medicines all carry the same underlying mechanism. Slower loss carries lower risk.

The second factor is specific to how these medicines work. GLP-1 receptor agonists delay stomach emptying, which reduces the hormonal signals that trigger the gallbladder to contract. A gallbladder that contracts infrequently doesn't flush itself out as often, and stagnant bile is where stones nucleate. Studies in the SURMOUNT and STEP clinical programmes identified gallbladder events (including gallstones and, less commonly, cholecystitis (gallbladder inflammation)) at rates higher than placebo, though still affecting a minority of participants. For a fuller look at what's known, including who may be at higher baseline risk, our dedicated page on using weight loss injections if you already have gallstones goes into more detail.

People who lost weight at the faster end of the response range, those with pre-existing metabolic risk factors, or those with a family history of gallbladder disease appear to carry higher individual risk. Worth checking.

What to watch for, and when to get medical help without delay

Most gallstones are silent, found incidentally on ultrasound, never causing symptoms. But some aren't. The warning signs that mean you should stop what you're doing and seek help the same day include:

• Sudden, severe pain in the upper right abdomen or just below the breastbone, lasting more than a few minutes
• Pain that spreads to the right shoulder or between the shoulder blades
• Nausea or vomiting alongside the pain
• Fever, chills or yellowing of the skin or eyes (jaundice) (these suggest the stone may have moved or the gallbladder has become inflamed

If you have fever and jaundice together, that's a potential emergency) call 999 or go to A&E. The MHRA's Yellow Card scheme at yellowcard.mhra.gov.uk is also where you can report any suspected side effect from a licensed medicine, including gallbladder symptoms you think may be linked to your treatment. Reports like that contribute to post-market safety monitoring for medicines still under additional MHRA surveillance, which both Mounjaro and Wegovy currently are.

Separately, it's worth knowing that not all upper abdominal discomfort on GLP-1 treatment is gallbladder-related. Reflux, slowed gut motility and nausea from the medicine itself can produce overlapping sensations. A prescriber can help distinguish them, which is exactly why ongoing clinical review matters, not just the initial consultation.

How prescribers assess this risk, and what happens next

Before treatment starts, a clinician considering your full picture will account for gallbladder history, current BMI, existing metabolic conditions and any family history of biliary disease. That's not a bureaucratic box-tick; it's the kind of individualised assessment that shapes whether treatment is appropriate and, if so, at what pace titration should proceed. Gradual dose increases give the body more time to adapt, and the rate of weight loss matters as much as the total amount.

If you're on treatment and develop confirmed gallstones, that doesn't necessarily mean stopping immediately, but it does mean a clinical conversation about how to proceed. Some people continue with monitoring; others pause or stop. That call belongs with a prescriber who knows your case. You can explore what the clinical conversation looks like on our page about taking weight loss injections with existing gallstones.

For those wondering how this compares to other possible complications, kidney stone risk is a separate question with a different mechanism, one that comes up often and is worth reading about if you have a history of urinary stones. And if you're still deciding whether injection-based treatment is the right route for you at all, our overview of weight loss injections in the UK covers the licensed options and how they differ. These are prescription medicines, and the right time to think through risks like gallstones is before your first pen arrives, not after. If you'd like a prescriber to review your circumstances, a free consultation is the first step.

Incidentally, if you do start treatment and your pen is dispatched, it arrives via DPD with tracking updates to your phone, in plain unbranded packaging. There's nothing to signal to anyone at the door what's inside. The clinical review that preceded it, though, is anything but anonymous, a named GPhC-registered prescriber read your consultation, not a piece of software.

Our free consultation page is where that process begins. Our clinical team is available to answer questions about your individual situation, including any gallbladder history that might be relevant, and if you're weighing up your options you can also read about Spire weight loss injections to see how different providers approach treatment.