Mounjaro (Tirzepatide): Side Effects, Risks and Safety Concerns

Mounjaro is a prescription drug with tirzepatide as its main ingredient. The FDA approved it in 2022 for adults with Type 2 diabetes.

Some doctors may also prescribe it for weight loss, even though that’s not technically what it’s approved for. This practice is called “off-label use.”

How Mounjaro Works — and Why That Matters for Safety

Mounjaro works by targeting two hormone receptors, GIP and GLP-1, simultaneously. This helps lower blood sugar and curb appetite, so many people lose weight while using it. However, because Mounjaro slows gastric emptying, it can sometimes cause serious digestive problems.

How Mounjaro Compares to Ozempic and Zepbound

Ozempic targets only the GLP-1 receptor, while Mounjaro and Zepbound use tirzepatide, which acts on both the GIP and GLP-1 receptors. In clinical trials, Mounjaro was very effective in lowering blood sugar and supporting weight loss.

Mounjaro side effects are primarily gastrointestinal-related and include nausea, vomiting and diarrhea. Serious side effects may include stomach paralysis, pancreatitis, acute kidney disease and other complications.

Mounjaro and Zepbound both have tirzepatide as their active ingredient. Both are manufactured by Eli Lilly. However, they are sold for different FDA-approved uses. Mounjaro is approved for Type 2 diabetes, while Zepbound is approved for weight loss.

Mounjaro may cause stomach-related side effects, especially when you first begin treatment or raise your dose. Most of these are minor and will typically ease over time.

Common Gastrointestinal Side Effects

In clinical trials, more people stopped taking Mounjaro because of stomach problems than people who took a placebo. These problems included nausea, vomiting and diarrhea. Most of these symptoms appeared when the dose was increased and became less common over time.

At least five out of every 100 people who used Mounjaro had these side effects.

These symptoms are usually at their worst when you start Mounjaro or increase your dose, but they often become milder over time.

Serious Side Effects Requiring Medical Attention

Stomach paralysis, or gastroparesis, is one of the most serious stomach problems linked to Mounjaro and is the main reason for related Mounjaro lawsuits. In addition, the drug label warns of the risk of several other serious Mounjaro side effects.

If you have severe stomach pain, nausea, or vomiting, seek medical help right away. Mounjaro may cause gallbladder problems, including gallstones or gallbladder inflammation. Severe allergic reactions are a medical emergency.

Black Box Warning — Thyroid Tumor Risk

Mounjaro has the FDA’s strongest warning about the risk of thyroid C-cell tumors, based on animal studies.

If you or someone in your family has had medullary thyroid carcinoma (MTC) or multiple endocrine neoplasia syndrome type 2 (MEN 2), you should not use Mounjaro. If you notice a lump in your neck, trouble swallowing or hoarseness, see a doctor right away.

Stomach paralysis, also called gastroparesis, happens when food does not move through the stomach as it should. This can cause problems like malnutrition, dehydration, unstable blood sugar, and in serious cases, may require hospitalization.

Mounjaro helps control blood sugar and reduce appetite by activating two hormones called GLP-1 and GIP. Because it targets both hormones, people may lose more weight with Mounjaro than with drugs like Ozempic and Wegovy, which only target one.

Mounjaro also slows stomach emptying, which is part of how tirzepatide works. Lawsuits claim this effect may cause or worsen gastroparesis in some people.

During the SURPASS trials, which assessed the safety of tirzepatide, many people taking tirzepatide experienced gastrointestinal side effects. Eli Lilly’s label also states that Mounjaro should not be used in people with gastroparesis.

In addition to gastroparesis, lawsuits about Mounjaro mention other stomach and intestinal problems like ileus, intestinal obstruction, intestinal pseudo-obstruction and ongoing vomiting. These issues can be hard to notice at first, so it is important not to ignore any new or worsening stomach symptoms after starting Mounjaro.

Since Mounjaro was approved, the FDA has updated its label several times to include safety information important for patients and anyone considering legal action. The warnings started with a black box warning about thyroid C-cell tumor risk and later included updates for hypersensitivity, pulmonary aspiration and acute kidney injury.

These label changes are important because they show that the FDA and the manufacturer keep updating safety information as new reports come in.

FDA Warnings on Compounded and Unapproved Versions

When GLP-1 drugs were in short supply, some compounding pharmacies made their own tirzepatide. This practice is often allowed during drug shortages.

However, the FDA says these versions are not checked for safety or quality, and some users reported health problems. By July 2025, the FDA had received 1,150 side-effect reports linked to unapproved GLP-1 drugs, including 545 related to compounded versions of Mounjaro.

The FDA advises that compounded versions of Mounjaro should be used only if an approved drug does not meet a patient’s medical needs. It recommends you get a prescription from your doctor and use a state-licensed pharmacy.

People claiming tirzepatide caused their stomach paralysis or other serious gastrointestinal injury have begun filing Mounjaro lawsuits.

As of June 2026, 3,763 lawsuits over GLP-1 drugs causing serious injuries have been combined into a multidistrict litigation (MDL) in the U.S. District Court for the Eastern District of Pennsylvania. MDLs allow several similar lawsuits to be consolidated into a single litigation, speeding up the legal process.

The lawsuits say that Mounjaro can cause serious stomach and intestinal problems, like stomach paralysis and blocked or paralyzed bowels. They also say that the drug company, Eli Lilly, did not do enough to warn people about these risks. If you took Mounjaro and had major stomach issues, you might have a case.