Mounjaro side effects

The label's table counts reactions reported by at least 5 in 100 people and more often than on placebo, pooled from two placebo-controlled trials in adults with 718 people on Mounjaro over a mean of 36.6 weeks. Every row below is from that table, at 5 mg, 10 mg, and 15 mg in that order, out of every 100 people, against 100 on placebo (Prescribing Information).

• Nausea: 12, 15, and 18, against 4 on placebo
• Diarrhea: 12, 13, and 17, against 9
• Decreased appetite: 5, 10, and 11, against 1
• Vomiting: 5, 5, and 9, against 2
• Constipation: 6, 6, and 7, against 1
• Indigestion: 8, 8, and 5, against 3
• Abdominal pain: 6, 5, and 5, against 4

Below the table's cutoff, the label lists burping in 2.5 to 3.3 in 100, gas in 1.3 to 2.9, reflux in 1.7 to 2.5, and bloating in 0.4 to 2.9, against under 1 in 100 on placebo for each (Prescribing Information). Counting every stomach-related reaction together, 37 in 100 at 5 mg, 40 in 100 at 10 mg, and 44 in 100 at 15 mg had at least one, against 20 in 100 on placebo (Prescribing Information). Three in 100 at 5 mg, 5 in 100 at 10 mg, and 7 in 100 at 15 mg stopped Mounjaro because of them, against fewer than 1 in 100 on placebo (Prescribing Information).

The cutoff on this table is 5 in 100. The Wegovy label reports at 2 in 100, so a shorter list means a narrower cutoff was used, and it says nothing about which drug is easier to take (Wegovy Prescribing Information). Zepbound is the same molecule under a different label, and its table reports different rates at the same milligram doses, because the two labels come from different trial populations and different indications (Zepbound Prescribing Information).

Other things the label puts a number on: injection site reactions in 3.2 in 100 adults on Mounjaro, acute gallbladder disease in 0.6 in 100 against none on placebo, adjudicated acute pancreatitis at 0.23 patients per 100 years of exposure against 0.11 on comparators, altered skin sensation in 0.4 in 100 at each dose, and a mean resting heart rate increase of 2 beats per minute (Prescribing Information).

The label puts the timing in one sentence. Most reports of nausea, vomiting, and diarrhea came during dose escalation and decreased over time (Prescribing Information). Lilly restates it the same way for patients (Mounjaro.lilly.com). That second half of the sentence belongs to this label in particular, because the semaglutide labels say only that reports clustered during escalation.

The schedule is the lever. The starting dose is 2.5 mg once weekly, which the label says is for treatment initiation and is not intended for blood sugar control, then 5 mg after 4 weeks, then increases of 2.5 mg at a time after at least 4 weeks on the current dose, up to a maximum of 15 mg once weekly in adults and 10 mg in children (Prescribing Information). The label says that escalation exists to reduce the risk of stomach reactions, and the pace of it belongs to your prescriber (Prescribing Information).

The label gives a small number of practical instructions, and these are the ones that come up in the first weeks.

• Once a week. Take it once weekly, at any time of day, with or without meals (Prescribing Information). You can move the day as long as at least 3 days, 72 hours, sit between the two doses (Prescribing Information).
• A missed dose. Take it as soon as possible within 4 days, 96 hours, of the missed dose. If more than 4 days have passed, skip it and take the next one on the regularly scheduled day (Prescribing Information). Never take two doses within 3 days of each other (Medication Guide). MedlinePlus gives the same two numbers (MedlinePlus).
• Where it goes. Inject under the skin of the abdomen or thigh, and use the back of the upper arm only when another person is giving the injection (Prescribing Information). Rotate the site with each dose (Prescribing Information). Never mix it with insulin, and if the two go in the same body region the injections should not sit next to each other (Prescribing Information). If you use vials, take a new syringe and needle for every injection (Prescribing Information).
• Birth control pills. Pills taken by mouth may not work as well while you use Mounjaro. Your prescriber may recommend another form of birth control for 4 weeks after you start and for 4 weeks after each increase in your dose (Medication Guide). Neither semaglutide product carries this instruction, so it is easy to miss when you read across GLP-1 pages.
• Drink fluids. Diarrhea, nausea, and vomiting can cost you fluids, and the label ties dehydration to kidney problems (Medication Guide).

The smaller-meals and bland-food advice you will see on other pages is not in the prescribing information or the Medication Guide. Lilly publishes it on the Mounjaro site instead (Mounjaro.lilly.com).

The Medication Guide, revised January 2026, sorts symptoms by how fast to move. These are its lines in plain form.

• Stop and get medical help right away: swelling of the face, lips, tongue, or throat, trouble breathing or swallowing, a severe rash or itching, fainting or dizziness, or a very rapid heartbeat (Medication Guide).
• Stop and call your prescriber right away: severe pain in your stomach area that will not go away, with or without nausea or vomiting, sometimes felt through to the back (Medication Guide).
• Tell your prescriber right away: pain in your upper stomach, fever, yellowing of the skin or eyes, or clay-colored stools, which can be symptoms of gallbladder problems (Medication Guide).
• Tell your prescriber right away: nausea, vomiting, or diarrhea that does not go away (Medication Guide).
• Tell your prescriber: a lump or swelling in your neck, hoarseness, trouble swallowing, or shortness of breath, which can be symptoms of thyroid cancer (Medication Guide).
• Tell your prescriber: stomach problems that are severe or will not go away, and any change in your vision during treatment (Medication Guide).
• Tell every provider you see that you take Mounjaro before surgery or any other procedure, because it may increase the chance of food getting into your lungs (Medication Guide).
• For too much Mounjaro, call your prescriber or the Poison Help line at 1-800-222-1222, or go to the nearest emergency room right away (Medication Guide). Call 911 if someone has collapsed, had a seizure, has trouble breathing, or cannot be woken (MedlinePlus).

Two parts of this label get misread often enough to be worth reading closely.

Low blood sugar is the first. In the 40-week trial of Mounjaro on its own, severe hypoglycemia was reported by nobody at any dose, and a reading under 54 mg/dL was reported by nobody on Mounjaro against 1 in 100 on placebo (Prescribing Information). Added to basal insulin over 40 weeks, readings under 54 mg/dL were reported by 16 in 100 at 5 mg, 19 in 100 at 10 mg, and 14 in 100 at 15 mg, against 13 in 100 on placebo, with severe lows in none, 2 in 100, and 1 in 100 (Prescribing Information). Taken with a sulfonylurea over as long as 104 weeks, readings under 54 mg/dL ran between 9.9 and 13.8 in 100 across the doses (Prescribing Information). The risk lives in those combinations, and the Medication Guide says the same thing in words: your risk of a low is higher if you use Mounjaro with insulin or a sulfonylurea (Medication Guide).

The eyes are where this label says less than people expect. It states that Mounjaro has not been studied in people with non-proliferative diabetic retinopathy requiring acute therapy, proliferative diabetic retinopathy, or diabetic macular edema, and that people with a history of diabetic retinopathy should be monitored for progression (Prescribing Information). There are no retinopathy rates in it at all. The 3 in 100 against 1.8 in 100 figures that circulate on GLP-1 pages come from the semaglutide labels and do not describe this drug (Ozempic and Wegovy Prescribing Information).

I never change your dose, never tell you to skip one, and never diagnose. What I do is ask every day how the nausea is, keep your answers with their dates, and when your pharmacy printout is on file hold what you tell me against its stop-and-call list so a bad turn gets noticed on the day it happens. I also keep shot day and the label's 4-day window against your real calendar, because a rule in a leaflet only helps if someone applies it to your actual week.

No clinician reviewed this page. It restates the FDA prescribing information and Medication Guide, Lilly's Mounjaro side-effects page, and MedlinePlus, linked below, and those are the documents to trust over anything here.