Mounjaro is tirzepatide, the same molecule as Zepbound, sold under the label written for type 2 diabetes. Its label is approved "as an adjunct to diet and exercise to improve glycemic control in adults and pediatric patients 10 years of age and older with type 2 diabetes mellitus", and, newer, "to reduce the risk of major adverse cardiovascular (CV) events" in adults with type 2 diabetes at high risk.1 That matters for this page: every side-effect number below comes from people with diabetes, many of them already on other glucose-lowering drugs. If you are looking at tirzepatide for weight loss without diabetes, the Zepbound numbers are the ones written for you, and we set them side by side further down.
Mounjaro side effects by dose: the label's table
The label's Table 1 pools the two placebo-controlled trials in adults (SURPASS-1, Mounjaro alone, and SURPASS-5, added to basal insulin) and lists every reaction that hit at least 5 percent of people on Mounjaro and was more common than on placebo. It leaves out low blood sugar, which has its own table.2
| Side effect | Placebo | Mounjaro 5 mg | Mounjaro 10 mg | Mounjaro 15 mg |
|---|---|---|---|---|
| Nausea | 4% | 12% | 15% | 18% |
| Diarrhea | 9% | 12% | 13% | 17% |
| Decreased appetite | 1% | 5% | 10% | 11% |
| Vomiting | 2% | 5% | 5% | 9% |
| Constipation | 1% | 6% | 6% | 7% |
| Dyspepsia (indigestion) | 3% | 8% | 8% | 5% |
| Abdominal pain | 4% | 6% | 5% | 5% |
Three things are worth reading out of that table. First, the pattern is dose-shaped for nausea, diarrhea, decreased appetite and vomiting: the higher the maintenance dose, the more people report it. Second, the gap over placebo is real but smaller than most people expect. Diarrhea runs 12 to 17 percent on Mounjaro, but 9 percent on placebo already had it, so the drug adds roughly 3 to 8 points. Third, "decreased appetite" is listed as a side effect because it is one in a diabetes trial. For many people it is the reason they are taking the drug.
The label also lists four gut effects that were more common on Mounjaro but under the 5 percent cut-off, given as placebo, 5 mg, 10 mg and 15 mg: "eructation (0.4%, 3.0%, 2.5%, 3.3%), flatulence (0%, 1.3%, 2.5%, 2.9%), gastroesophageal reflux disease (0.4%, 1.7%, 2.5%, 1.7%), abdominal distension (0.4%, 0.4%, 2.9%, 0.8%)."3 Eructation is burping, the one people notice most and the one the label quietly puts a number on.
The stomach side effects: how common, how long, and who stops
Counting every gastrointestinal reaction together, the label gives the clearest single picture of what to expect: reactions "occurred more frequently among patients receiving MOUNJARO than placebo (placebo 20.4%, MOUNJARO 5 mg 37.1%, MOUNJARO 10 mg 39.6%, MOUNJARO 15 mg 43.6%)".3 Put plainly, somewhere between one in three and a little under one in two people on Mounjaro had at least one stomach complaint, against one in five on placebo.
Two sentences in the same paragraph are the ones that change how this feels in practice. On timing: "The majority of reports of nausea, vomiting, and/or diarrhea occurred during dose escalation and decreased over time." On quitting: "More patients receiving MOUNJARO 5 mg (3.0%), MOUNJARO 10 mg (5.4%), and MOUNJARO 15 mg (6.6%) discontinued treatment due to gastrointestinal adverse reactions than patients receiving placebo (0.4%)."3 So the large majority of people who get nausea keep going, and the label's own explanation for its slow start is exactly this: the escalation schedule exists "to reduce the risk of gastrointestinal adverse reactions".11 How fast to climb is your prescriber's call, not ours, and not something to change on your own.
The rarer, severe end has its own number in the warnings section: "severe gastrointestinal adverse reactions occurred more frequently among patients receiving MOUNJARO (5 mg 1.3%, 10 mg 0.4%, 15 mg 1.2%) than placebo (0.9%)." The same section adds one hard line: "MOUNJARO is not recommended in patients with severe gastroparesis."7 Our guide to nausea, constipation and diarrhea on a GLP-1 covers what people actually do about the common, mild end.
In the big heart trial, a few numbers moved
Mounjaro's cardiovascular outcomes trial enrolled 6,647 adults with type 2 diabetes and established heart disease, a sicker and older group than the approval trials. The label reports that side effects there "were similar with the exception of dysesthesia (0.7%), decreased appetite (17%), constipation (13%), vomiting (12%), abdominal pain (10%), and fatigue (10%)".4 Constipation and fatigue are the two to notice: both run higher in that trial than in the pooled table, which is a reasonable warning that real-world patients with more health problems may see more of them.
Low blood sugar: rare on Mounjaro alone, real with insulin or a sulfonylurea
Tirzepatide raises insulin release only when blood sugar is up, which is why low blood sugar on Mounjaro alone is uncommon. The label's Table 2 shows it directly. In the 40-week trial of Mounjaro alone, readings below 54 mg/dL happened in 1 percent of people on placebo and 0 percent at every Mounjaro dose, with no severe episodes in any group.5
| Trial (40 weeks) | Event | Placebo | 5 mg | 10 mg | 15 mg |
|---|---|---|---|---|---|
| Mounjaro alone | Blood glucose below 54 mg/dL | 1% | 0% | 0% | 0% |
| Mounjaro alone | Severe hypoglycemia | 0% | 0% | 0% | 0% |
| Added to basal insulin | Blood glucose below 54 mg/dL | 13% | 16% | 19% | 14% |
| Added to basal insulin | Severe hypoglycemia | 0% | 0% | 2% | 1% |
The insulin rows are the ones that matter if you already inject insulin. And sulfonylureas, the older pills such as glipizide and glimepiride, carry the same risk: "Hypoglycemia was more frequent when MOUNJARO was used in combination with a sulfonylurea". In a trial of up to 104 weeks, "when administered with a sulfonylurea, hypoglycemia (glucose level <54 mg/dL) occurred in 13.8%, 9.9%, and 12.8%, and severe hypoglycemia occurred in 0.5%, 0%, and 0.6% of patients treated with MOUNJARO 5 mg, 10 mg, and 15 mg, respectively."5 Severe here means someone else had to help you. This is the single most practical safety point on the label for people with diabetes: if you take insulin or a sulfonylurea, the doses of those drugs are what your prescriber may adjust, and the signs of a low are worth knowing before the first injection.
Less common side effects, with the label's numbers
The label gives a figure for each of these from the placebo-controlled pool, and they are worth knowing because several of them are the reason people search this topic at 2am.6
| Side effect | What the label reports |
|---|---|
| Injection site reactions | 3.2% on Mounjaro vs 0.4% on placebo |
| Allergic (hypersensitivity) reactions | 3.2% vs 1.7%, sometimes severe (for example hives and eczema) |
| Heart rate | A mean increase of 2 to 4 beats per minute vs 1 on placebo |
| Gallbladder problems (stones, biliary colic, removal) | 0.6% vs 0% |
| Acute pancreatitis (confirmed) | 0.23 patients per 100 years of exposure vs 0.11 on comparators |
| Dysesthesia (abnormal skin sensation) | 0.4% at each dose vs none on placebo |
Read the pancreatitis line carefully: it is a rate per 100 years of exposure, not a percentage of patients, because it is rare enough that the trials counted it that way. The label puts it in plain numbers too: "14 events of acute pancreatitis were confirmed by adjudication in 13 MOUNJARO-treated adult patients".6
The serious warnings: what to watch for and when to call
The warnings section is where the label tells prescribers what to tell you. These are rare, but they are the side effects that need a call rather than patience.7
- Pancreatitis. The label's description of the symptom is specific: "persistent or severe abdominal pain (sometimes radiating to the back) and which may or may not be accompanied by nausea or vomiting." The postmarketing list adds that this has included "hemorrhagic and necrotizing pancreatitis sometimes resulting in death".8
- Kidney injury from dehydration. "There have been postmarketing reports of acute kidney injury, in some cases requiring hemodialysis", and "the majority of the reported events occurred in patients who experienced gastrointestinal adverse reactions leading to dehydration such as nausea, vomiting, or diarrhea". This is the reason heavy vomiting or diarrhea is not something to sit out.
- Gallbladder disease. Covered in the table above; pain under the right ribs, often after eating, is the classic sign.
- Diabetic eye disease. "Temporary worsening of diabetic retinopathy has been reported with rapid improvement in glucose control." Anyone with known retinopathy is meant to be monitored.
- Surgery and sedation. Because Mounjaro slows stomach emptying, "there have been rare postmarketing reports of pulmonary aspiration" during procedures under general anesthesia or deep sedation. The label's instruction is simple: tell the team doing the procedure that you take Mounjaro.
- Thyroid. Mounjaro carries a boxed warning based on thyroid C-cell tumors seen in preclinical studies. The label is explicit that "it is unknown whether MOUNJARO causes thyroid C-cell tumors, including medullary thyroid carcinoma (MTC), in humans", that it is contraindicated with a personal or family history of MTC or MEN 2, and that the symptoms to report are "a mass in the neck, dysphagia, dyspnea, persistent hoarseness".
The postmarketing section, which lists reports from real-world use where the label says "it is not always possible to reliably estimate their frequency or establish a causal relationship", also names "ileus, intestinal obstruction, severe constipation including fecal impaction", serious allergic reactions ("anaphylaxis, angioedema"), kidney failure, and "alopecia", meaning hair loss.8 Hair loss on these drugs tracks the speed of weight loss; our GLP-1 hair loss guide has the numbers from the trials that measured it.
Mounjaro and the birth control pill
This one is easy to miss and is printed in the drug interactions section. Mounjaro "delays gastric emptying and thereby has the potential to impact the absorption of concomitantly administered oral medications", and for the pill specifically the label says: "Advise patients using oral hormonal contraceptives to switch to a non-oral contraceptive method or add a barrier method of contraception for 4 weeks after initiation and for 4 weeks after each dose escalation with MOUNJARO. Hormonal contraceptives that are not administered orally should not be affected".9 An IUD, implant, patch or ring is not affected; the pill needs a backup during those windows.
Children and teenagers
Mounjaro is approved from age 10 for type 2 diabetes, and the paediatric trial looked mostly like the adult one, with two exceptions the label quantifies: "vomiting occurred in 3%, 16%, and 12% of patients and abdominal pain occurred in 9%, 22%, and 15% of patients treated with placebo, MOUNJARO 5 mg, and 10 mg, respectively."10 Vomiting and stomach pain ran noticeably higher in younger patients than in adults.
Tirzepatide side effects: Mounjaro vs Zepbound
Mounjaro and Zepbound are the same drug. Tirzepatide "is a GIP receptor and GLP-1 receptor agonist" that "selectively binds to and activates both the GIP and GLP-1 receptors", and on Mounjaro's own label it "decreases food intake, and reduces body weight in patients with type 2 diabetes mellitus".11 Zepbound's label states it outright: "ZEPBOUND contains tirzepatide", and taking it with another tirzepatide product or any GLP-1 drug "is not recommended".12 Yet the two labels print noticeably different side-effect rates.
| Measure | Mounjaro label (type 2 diabetes trials) | Zepbound label (weight-loss trials) |
|---|---|---|
| Nausea, 5 / 10 / 15 mg | 12% / 15% / 18% (placebo 4%) | 25% / 29% / 28% (placebo 8%) |
| Vomiting, 5 / 10 / 15 mg | 5% / 5% / 9% (placebo 2%) | 8% / 11% / 13% (placebo 2%) |
| Any stomach reaction | 37.1% / 39.6% / 43.6% (placebo 20.4%) | 56% at every dose (placebo 30%) |
| Stopped because of side effects | 3.0% / 5.4% / 6.6% for stomach reactions (placebo 0.4%) | 4.8% / 6.3% / 6.7% for any reaction (placebo 3.4%) |
Why the gap? The populations and the trials differ: the Zepbound trials enrolled adults with obesity, most without diabetes, followed for longer, and their tables count reactions down to 2 percent rather than 5. The Mounjaro label itself warns against reading too much into a side-by-side like this: "adverse reaction rates observed in the clinical trials of a drug cannot be directly compared to rates in the clinical trials of another drug and may not reflect the rates observed in practice."10 The fair summary is that tirzepatide's side effects are the same kind on both labels, mostly stomach effects during escalation, and that people taking it for weight loss in the Zepbound trials reported them more often. The full Zepbound table is in our Zepbound side effects guide, and the case for each brand is in Mounjaro for weight loss.
What the side effects mean for what you pay
Side effects shape the bill more than most people expect, for one reason: they decide how long you stay on the lower, cheaper steps. Brand pricing climbs with the dose, compounded programs often charge one price at every dose, and a plan you prepay for a year still costs the same if nausea makes you stop in month two. Before you commit to a long prepaid plan, check whether the seller lets you cancel, and compare what every tirzepatide program charges today:
Compounded tirzepatide is the same molecule but is not FDA-approved, and its side effects have not been studied the way Mounjaro's were; our guide to compounded tirzepatide explains what that does and does not change. Everything on this page is quoted from the label; it is not medical advice, and the person who can tell you whether a side effect is normal for you is the clinician who prescribed it.
