Weight loss injections such as Wegovy and Mounjaro have changed the way obesity and weight management can be treated. For many people, these medicines can result in significant weight loss and improvements in weight-related health conditions.

However, like all medications, they can have side effects. One potential complication that people using weight loss injections should be aware of is gallstones and other gallbladder problems.

This has recently received attention in New Zealand. In September 2026, Medsafe highlighted an adverse-reaction report involving a patient who developed cholecystitis (inflammation of the gallbladder) several months after starting semaglutide.

So, can weight loss injections cause gallstones, how significant is the risk, and what symptoms should you look out for?

Can Weight Loss Injections Cause Gallstones?

Research has found an association between GLP-1 receptor agonist medicines and an increased risk of gallbladder and biliary disease.

These medicines include semaglutide, the active ingredient in Wegovy, as well as other medications used in the management of diabetes and obesity.

In its September 2026 update, Medsafe reported that the Wegovy data sheet states that cholelithiasis (gallstones) occurred in 1.6% of patients and cholecystitis in 0.6% of patients treated with semaglutide.

It's important to put this into perspective. Most people taking these medications will not develop gallbladder disease. However, it is a recognised potential complication and one that patients should know about.

What Has Medsafe Reported in New Zealand?

Medsafe, New Zealand's medicines and medical devices safety authority, regularly reviews reports of suspected adverse reactions to medicines.

In September 2026, Medsafe highlighted the case of a 39-year-old woman who developed cholecystitis several months after starting semaglutide.

A report of an adverse reaction does not by itself prove that a medicine caused the condition. These reports are used to help identify and monitor potential safety issues.

However, gallbladder complications are already recognised in the prescribing information for semaglutide, and evidence from clinical trials has also identified an association between GLP-1 receptor agonists and gallbladder disease.

Why Can Weight Loss Increase the Risk of Gallstones?

The relationship isn't necessarily as simple as a particular medicine directly causing a gallstone.

Rapid or substantial weight loss itself is a known risk factor for gallstones.

When someone loses weight quickly, changes can occur in the composition of bile and the way the gallbladder empties. This can make it easier for cholesterol crystals to develop and eventually form gallstones.

This phenomenon isn't unique to weight loss injections. An increased risk of gallstones can also occur following substantial weight loss through other methods, including after bariatric surgery.

There may also be effects associated with GLP-1 receptor agonists themselves. Research has suggested these medicines can affect gallbladder motility and emptying.

A large systematic review and meta-analysis involving more than 100,000 participants across 76 randomised clinical trials found GLP-1 receptor agonist treatment was associated with an increased risk of gallbladder or biliary disease. The association was particularly evident in trials where these medicines were being used for weight loss, at higher doses and for longer periods.

The overall absolute increase in risk was relatively small, however, which is important when considering these findings alongside the potential benefits of treatment.

What Are Gallstones?

The gallbladder is a small organ located underneath the liver. It stores bile, which helps your body digest fats.

Gallstones are hardened deposits that develop inside the gallbladder.

Many people have gallstones without ever knowing it. If the stones remain inside the gallbladder without obstructing anything, they may cause no symptoms at all.

Problems can develop when a gallstone moves and blocks the exit from the gallbladder or one of the bile ducts.

This can cause significant pain and, in some cases, complications requiring urgent medical treatment.

What Are the Symptoms of Gallstones?

The classic symptom of symptomatic gallstones is pain in the upper abdomen, particularly towards the right-hand side.

The pain may:

• Become quite severe

• Occur after eating, particularly after a fatty meal

• Spread towards the back or right shoulder

• Last for several hours

• Be accompanied by nausea or vomiting

This type of pain is often referred to as biliary colic.

If you've recently started weight loss medication and develop new or recurrent upper abdominal pain, it's worth discussing this with your healthcare provider.

What Is Cholecystitis?

Cholecystitis means inflammation of the gallbladder.

It most commonly occurs when a gallstone blocks the outlet from the gallbladder. The blockage can cause the gallbladder to become inflamed and sometimes infected.

Unlike biliary colic, where the pain may eventually settle, cholecystitis can produce more persistent and severe pain.

Symptoms can include:

• Severe or persistent upper-right abdominal pain

• Pain spreading towards the back or shoulder

• Nausea or vomiting

• Fever

• Tenderness over the upper abdomen

• Feeling generally unwell

• Cholecystitis often requires assessment and treatment in hospital.

When Should Someone Taking Wegovy or Mounjaro Seek Medical Advice?

Health New Zealand advises people using injected weight-loss medicines to seek medical help if they experience symptoms including severe pain in the abdomen and back accompanied by nausea and vomiting.

You should also seek medical attention for abdominal pain accompanied by yellowing of the skin or eyes (jaundice), or unusually pale stools.

These symptoms can indicate a problem involving the gallbladder, bile ducts or pancreas and shouldn't simply be assumed to be the normal gastrointestinal side effects of weight loss medication.

This distinction is important because nausea, changes in bowel habits and mild abdominal discomfort can occur with GLP-1 medicines, particularly when treatment begins or the dose is increased.

Severe or persistent abdominal pain is different and deserves medical assessment.

Are Gallstones Dangerous?

Gallstones themselves aren't necessarily dangerous. Many people have them without symptoms and require no treatment.

Problems occur when stones obstruct the normal flow of bile.

Potential complications include:

Cholecystitis – inflammation of the gallbladder.

Cholangitis – infection involving the bile ducts.

Pancreatitis – inflammation of the pancreas, which can occur if a gallstone obstructs the area where the pancreatic duct drains.

Jaundice – yellowing of the skin and eyes resulting from obstruction of bile flow.

Some of these complications can be serious and require urgent hospital treatment.

How Are Gallstones Diagnosed?

If your symptoms suggest gallstones, your healthcare provider will normally take a medical history and examine your abdomen.

An ultrasound scan is commonly used to look for stones inside the gallbladder.

Depending on the symptoms and findings, blood tests or additional imaging may also be required, particularly if there's concern that a stone has moved into the main bile duct.

Do Gallstones Always Require Surgery?

No.

Gallstones that aren't causing symptoms frequently don't require treatment.

However, recurrent pain or complications such as cholecystitis can lead to consideration of removing the gallbladder.

The most common operation is a laparoscopic cholecystectomy, commonly known as keyhole gallbladder surgery.

During the procedure, the gallbladder is removed through several small incisions in the abdomen.

People can live normally without a gallbladder. Bile simply travels directly from the liver into the intestine rather than being stored in the gallbladder.

Should I Stop Taking Weight Loss Injections If I Have Gallbladder Symptoms?

Don't stop or alter prescribed medication without discussing it with the healthcare professional managing your treatment, unless you've been instructed to do so.

New or significant abdominal symptoms should instead prompt medical assessment.

Your healthcare provider can consider your symptoms, medical history, weight loss, medication and any investigation results before determining the appropriate next step.

The presence of a potential side effect also doesn't mean that medications such as Wegovy or Mounjaro are inherently unsafe.

For appropriately selected patients, weight loss medications can offer meaningful health benefits. The important thing is understanding both their benefits and their potential risks and having appropriate medical supervision.

Does Rapid Weight Loss Increase the Risk of Gallstones?

Yes. Rapid weight loss is itself associated with an increased risk of gallstone formation.

Health New Zealand recommends that people who are overweight and trying to reduce their risk of gallstone attacks lose weight gradually rather than very rapidly.

This is another reason weight management should focus on long-term health rather than simply achieving the fastest possible reduction on the scales.

Weight Loss Injections, Gallstones and Weight Loss Surgery

People considering treatment for obesity now have more options than ever before.

For some, medication may be appropriate. For others with significant obesity or obesity-related health problems, bariatric surgery such as sleeve gastrectomy or gastric bypass may be considered.

Both approaches have benefits, limitations and potential complications.

Importantly, significant weight loss itself — whether achieved medically or surgically — can influence gallstone risk.

The appropriate treatment therefore depends on the individual, their health, BMI, previous attempts at weight loss and their longer-term goals.

Gallbladder and Weight Loss Surgery Advice in Tauranga

If you develop persistent or recurrent symptoms that may be related to gallstones, it's important to obtain an appropriate diagnosis rather than simply managing the pain yourself.

At Bay Surgery in Tauranga, our specialists provide assessment and surgical treatment for a range of conditions, including gallbladder disease, as well as specialist bariatric surgery for appropriate patients considering surgical weight-loss options.

Understanding why symptoms are occurring is the first step towards determining whether treatment is required.

Frequently Asked Questions

Can Wegovy cause gallstones?

Gallstones are a recognised potential adverse effect associated with semaglutide treatment. Medsafe reports that the Wegovy data sheet records cholelithiasis in 1.6% of treated patients. However, most people taking Wegovy will not develop gallstones.

Can Mounjaro cause gallbladder problems?

Health New Zealand includes gallbladder problems among the less common but potentially serious side effects people taking injected weight-loss medicines such as Wegovy and Mounjaro should be aware of.

Why does rapid weight loss cause gallstones?

Rapid weight loss can change the composition of bile and how effectively the gallbladder empties, which can encourage gallstone formation.

Where does gallbladder pain occur?

Gallbladder pain is typically felt in the upper-right area of the abdomen and may spread through to the back or towards the right shoulder. It may occur after eating and can be accompanied by nausea or vomiting.

What should I do if I get severe abdominal pain while taking Wegovy or Mounjaro?

Seek medical advice. Health New Zealand recommends immediate contact with a healthcare provider or Healthline for severe abdominal and back pain accompanied by nausea and vomiting.

Can you live normally without a gallbladder?

Yes. Most people live normally without their gallbladder. The liver continues producing bile, which flows directly into the intestine rather than being stored in the gallbladder.

Do weight loss injections need to be stopped before surgery?

If you're taking Wegovy or Mounjaro and are due to have an operation, tell your surgeon, anaesthetist and healthcare team. These medicines slow stomach emptying, which is relevant to anaesthesia and surgical planning. Your medical team can advise you on what to do with your medication before the procedure.

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