Mounjaro Side Effects: What to Expect, How Long They Last and How to Track Them
The most common Mounjaro side effects are nausea, diarrhea, constipation and vomiting, and for most people they're temporary, strongest in the first weeks and easing as the body gets used to each dose. Mounjaro contains tirzepatide, and in weight-loss trials of this GLP-1 medication up to 29% of people had nausea, mostly while the dose was being increased (Zepbound prescribing information). That first stretch is very manageable once you know what to expect. Glapp, a GLP-1 tracking app, lets you log every side effect right next to your Mounjaro doses, so you can see your own pattern and watch it fade.
Key numbers
| Number | What it means |
|---|---|
| 25–29% | of people on tirzepatide had nausea in weight-loss trials, the most common side effect, vs 8% on placebo |
| 15,093 | users currently tracking Mounjaro side effects in Glapp |
| 1.7–3.1% | had a severe stomach side effect, vs 1% on placebo: most side effects stayed manageable |
Mounjaro side effects: what the clinical trials show
Mounjaro and Zepbound are two brands of the same molecule, tirzepatide, both made by Eli Lilly. Zepbound is the one approved for weight loss, so its trials give the clearest picture for anyone using tirzepatide to lose weight. In the two pooled weight-loss trials behind Zepbound's prescribing information (958 people on placebo, 2,519 on tirzepatide), the most common side effects were:
| Side effect | Placebo | 5 mg | 10 mg | 15 mg |
|---|---|---|---|---|
| Nausea | 8% | 25% | 29% | 28% |
| Diarrhea | 8% | 19% | 21% | 23% |
| Vomiting | 2% | 8% | 11% | 13% |
| Constipation | 5% | 17% | 14% | 11% |
| Abdominal pain | 5% | 9% | 9% | 10% |
| Indigestion (dyspepsia) | 4% | 9% | 9% | 10% |
| Injection site reactions | 2% | 6% | 8% | 8% |
| Fatigue | 3% | 5% | 6% | 7% |
| Hair loss | 1% | 5% | 4% | 5% |
| Dizziness | 2% | 4% | 5% | 4% |
Source: Zepbound prescribing information, Table 1. The full list of 16 side effects is on Zepbound side effects.
Most nausea, vomiting and diarrhea happened during dose escalation and decreased over time, and more than 9 in 10 people stayed on treatment. In SURMOUNT-1, people on tirzepatide lost 15–20.9% of their body weight over 72 weeks, vs 3.1% on placebo, so the side effects come alongside some of the largest weight loss seen with any GLP-1 medication.
Common Mounjaro side effects, one by one
Each of these has its own guide with the full data, the causes and a tracking plan.
- Nausea (25–29%). The most common side effect, usually worst in the first day or two after a shot. Full guide
- Diarrhea (19–23%). Mostly while the dose is going up; fluids and electrolytes matter most. Full guide
- Vomiting (8–13%). Rises with dose and usually travels with nausea. Full guide
- Constipation (11–17%). Most common at the lowest dose, not the highest; fiber, fluids and movement help. Full guide
- Heartburn, indigestion and burping (4–10%). Food stays in the stomach longer. Full guide
- Fatigue (5–7%). Often linked to eating and drinking much less in the first weeks. Full guide
- Injection site reactions (6–8%). Redness, itching or bruising where the needle went in, usually gone within days. Full guide
- Hair loss (4–5%). Temporary shedding (telogen effluvium) a few months in, linked to fast weight loss. Full guide
- Headaches. Not among the common side effects in the trials, but often linked to dehydration and skipped meals. Full guide
- Dizziness (4–5%). More likely when you're dehydrated or your blood pressure falls as you lose weight.
Why does Mounjaro cause side effects?
Mounjaro (tirzepatide) is the first dual GIP and GLP-1 receptor agonist. It copies two gut hormones, called incretins, that signal fullness to the brain and slow how quickly the stomach empties (gastric emptying). That's how it cuts appetite and food noise, and it's also where most side effects come from:
- Slower gastric emptying brings fullness, nausea, burping, heartburn and constipation.
- A gut that's adjusting brings diarrhea, bloating and gas, mostly in the first weeks of each dose.
- Eating far less means fewer calories, less fluid and often less protein, which can lead to tiredness, dizziness, headaches and, a few months in, hair shedding.
- Dose steps restart the adjustment, so side effects tend to return for a week or two after each increase.
How long do Mounjaro side effects last?
For most people, Mounjaro side effects last a few weeks, not months. They're strongest right after you start and after each dose increase, peak in the first one to three days after each shot, and fade as your body adjusts. Tirzepatide reaches its highest level a median of 24 hours after an injection (range 8–72 hours) and settles into a steady weekly level after about four weeks at the same dose, so by the fourth week on a dose most people feel noticeably better than in the first.
Mounjaro side effects in the first week
The first week on 2.5 mg is usually the mildest it gets, because 2.5 mg is a starter dose. Expect some fullness, a smaller appetite and possibly nausea or loose stools a day or two after the shot. Many people find these settle by the end of the first month, then come back briefly at 5 mg.
| Side effect | How long it usually lasts | When to call your prescriber |
|---|---|---|
| Nausea | A day or two after each shot; eases over a few weeks at a stable dose | You can't keep food or fluids down |
| Diarrhea | A few days per episode, mostly during dose escalation | It lasts more than a couple of days, or comes with blood, fever or dizziness |
| Constipation | Can linger longer than other stomach side effects | No bowel movement for more than three days, or severe pain |
| Fatigue | The first weeks and after each dose step | It doesn't lift after a few weeks on the same dose |
| Hair loss | Starts two to four months in; regrowth within six to twelve months | Shedding lasts more than six months or comes in patches |
Tirzepatide's half-life is about five days, so after a last dose it takes around a month to leave your body.
Track your Mounjaro side effects with a Mounjaro progress tracker and stay in control: your 30-day plan
The first month on Mounjaro is when side effects are most likely and hardest to read. An injection app like Glapp makes it simple: log how you feel each day next to your Mounjaro doses, and you're in control. You'll know which day after your shot each side effect peaks, whether a dose step brought it on and whether it's easing, and you'll walk into your next appointment with facts instead of guesses.
Why Glapp? It's a top-rated GLP-1 app and dose tracker used by 100,000+ people, rated 4.8/5 on Trustpilot and the App Store, and 4.6/5 on Google Play. Glapp grew out of Reddit GLP-1 support groups and is built by people who take GLP-1 medications themselves, so most of what's in it came straight from what the community asked for: daily side-effect check-ins, an estimated Mounjaro level, custom titration curves for your dose steps and a doctor's report you can share. It's grounded in published clinical trial data and peer-reviewed research, core tracking is free, and it syncs across iPhone, Android and web. Here's how to use it over your first 30 days.
Glapp does not provide medical advice or treat side effects. It shows your daily check-ins against your estimated medication levels so you have structured data to share with your prescriber.
Day 1: Start tracking your side effects
Use Glapp's daily check-in to record any side effect you notice, from nausea to tiredness, and rate how severe it feels. Log your Mounjaro dose and injection time too, so everything that follows is based on what you actually took.
Daily entries help you see whether each side effect is getting better, getting worse or staying the same. You'll have a clear record of how you felt, without having to remember every day.
Day 3: Compare symptoms with your estimated Mounjaro level
Glapp estimates your medication level throughout the day using your dose and injection time. Mounjaro typically reaches its highest blood concentration 8–72 hours after an injection.
Seeing your symptoms alongside this estimate helps you spot when each side effect appears within your shot cycle. As you log more days, you can look for a repeating pattern and know when to pay closer attention.
The medication level is an estimate, not a blood test, and a matching pattern does not prove what caused your symptoms.
Day 7: See how your side effects change over time
Open the side-effects chart in the Progress tab and choose the period you want to review. Your daily ratings appear on a timeline, making it easier to see whether a difficult day was an isolated episode or part of a longer trend.
Day 14: Look for patterns in your weekly report
Glapp's weekly progress report brings your logged data together, with dedicated sections showing your side effects and how they change.
Do side effects return on the same day after your shot? Did they start after a dose step? Do they coincide with changes in hunger or food noise? Reviewing two weeks of entries can help you spot patterns that are easy to miss day by day, and give you specific questions to discuss with your doctor.
Day 30: Bring a clear record to your doctor
After a month, review the bigger picture: are your side effects becoming less frequent, staying the same or getting worse? Mounjaro generally reaches a steady repeating level after about four weeks of weekly injections at the same dose, which is usually when the first step up is discussed.
Create a doctor's report in Glapp and choose the information to include. Your doctor can review your symptom history alongside your doses and progress, giving you a more focused conversation about your treatment and your next dose step.
Start tracking your Mounjaro side effects in Glapp
Mounjaro side effects by dose: what changes at each step
Mounjaro starts at 2.5 mg once a week for four weeks, then goes up in 2.5 mg steps, at least four weeks apart, up to a maximum of 15 mg.
| 5 mg | 10 mg | 15 mg | |
|---|---|---|---|
| Nausea | 25% | 29% | 28% |
| Diarrhea | 19% | 21% | 23% |
| Vomiting | 8% | 11% | 13% |
| Constipation | 17% | 14% | 11% |
| Severe stomach side effects | 1.7% | 2.5% | 3.1% |
| Stopped because of stomach side effects | 1.9% | 3.3% | 4.3% |
Tirzepatide weight-loss trials; placebo: 1% severe stomach side effects, 0.5% stopped because of them. Source: Zepbound prescribing information.
Higher doses brought a little more nausea, diarrhea and vomiting, while constipation eased. The two weeks after each step are when side effects are most likely, so that's when your check-ins tell you the most.
What to bring to your prescriber
Glapp's doctor's report puts your side effects, doses and progress on one page. Before your appointment, check it shows:
- which side effects you had and how severe they were
- which day after your shot they peaked
- whether they started after a dose step
- any day you couldn't eat or keep fluids down
Questions you could ask. They're conversation starters, not recommendations; your prescriber decides what, if anything, to change.
- "My nausea is worst the day after my shot. Is that expected on Mounjaro?"
- "Should I stay on this dose longer before my next step?"
- "Which side effects should make me call you straight away?"
Frequently asked questions
How long do Mounjaro side effects last?
Usually a few weeks per dose. Side effects are strongest in the first one to two weeks after starting and after each increase, peak one to three days after each shot, and ease once you've been on the same dose for about four weeks. Hair shedding is the exception: it starts later and takes months to grow back.
What are the side effects of Mounjaro in the first week?
On the 2.5 mg starter dose, the most common are a smaller appetite, fullness, mild nausea and loose stools, usually a day or two after the shot. For many people the first week is the gentlest, and side effects are more likely after the first step to 5 mg.
Are Mounjaro and Zepbound side effects the same?
Yes. Both contain tirzepatide at the same doses, so the same side effects are expected. Zepbound is the version approved for weight loss, which is why its trials are the source for weight-loss side-effect rates. See Zepbound side effects.
Do Mounjaro side effects go away?
Yes, for most people. In the trials, most nausea, vomiting and diarrhea happened during dose escalation and decreased over time, and more than 9 in 10 people stayed on treatment.
What are the serious side effects of Mounjaro?
Rare but serious ones include pancreatitis, gallbladder problems, dehydration leading to kidney injury, serious allergic reactions and, in animal studies, thyroid C-cell tumors. Severe stomach pain, vomiting you can't stop or swelling of the face or throat need urgent care.
How do I track Mounjaro side effects?
Log them in Glapp's daily check-in and rate each one low, medium or high, next to your Mounjaro dose. Glapp shows each rating against your estimated medication level, and your weekly reports show which day after the shot each side effect peaks.
About the data
Ratings are self-reported and medication levels are estimated from dose and timing, not measured. Trial figures come from FDA-approved tirzepatide weight-loss trials. This page is for information only and is not medical advice; talk to your prescriber about any side effect.
About the author
We're GLP-1 patients and health tech professionals, building Glapp in collaboration with doctors. About us
Sources
- Eli Lilly. Zepbound (tirzepatide) prescribing information: Table 1, warnings and precautions, dosage, pharmacokinetics.
- Jastreboff AM, et al. Tirzepatide once weekly for the treatment of obesity (SURMOUNT-1). N Engl J Med. 2022;387:205–16. Trial summary.
- Eli Lilly. Mounjaro (tirzepatide) prescribing information: dosage and administration.