Wegovy® and Mounjaro® side effects are mostly digestive, cluster around dose increases, and are mostly mild to moderate in severity per the official product information. Around 44% of people on semaglutide and 25–33% on tirzepatide (depending on dose) experience nausea at some point (figures from separate trials that cannot be compared directly). But a nausea episode lasts a median of 8 days, and the vast majority of patients stay on treatment. Here is what the official documents and trials actually say, week by week.
⚕️ This article summarizes official EMA product information and published trials, for information only. It replaces neither your medication leaflet nor advice from your doctor or pharmacist.
The 30-second version
- What? Nausea, diarrhea, constipation, vomiting, abdominal pain: “very common” in both SmPCs; headache and fatigue join the list for Wegovy
- When? Mostly during dose escalation; the overall peak sits around week 20 (semaglutide data, STEP trials), then frequency drops sharply
- How long? A nausea episode lasts a median of 8 days, a diarrhea episode 3 days; constipation lingers longer (median 47 days)
- Does it pass? Per Wegovy’s leaflet, these effects usually go away over time; 2–4% of patients stop because of digestive effects, depending on drug and dose
- Useful reflexes: you and your doctor can slow the titration ladder, hydration is non-negotiable, bland food on rough days
- Seek help immediately for severe, persistent stomach pain that may radiate to the back (possible pancreatitis), verbatim from the leaflets
Why side effects cluster in the first weeks
Both treatments deliberately start very low (0.25 mg for Wegovy, 2.5 mg for Mounjaro), precisely to limit digestive effects. Wegovy’s SmPC spells it out: the dose is raised over a 16-week period precisely to reduce the likelihood of gastrointestinal symptoms. Each step up reopens a sensitive window: pooled analyses of the STEP trials show the vast majority of patients experience their first digestive effect during the dose-escalation period.
Worth knowing: contrary to popular belief, studies do not describe a “spike” after each individual injection. At a stable dose, drug levels even out from one week to the next. It is the dose steps that matter.
Week by week: what to expect
Weeks 1–4: the start (0.25 mg / 2.5 mg). A deliberately low priming dose. The first digestive effects can appear; per Mounjaro’s leaflet, they are usually not severe.
At every step up (every 4 weeks at the earliest): statistically the most sensitive period for nausea, vomiting and diarrhea. Mounjaro’s SmPC states that their incidence was higher during dose escalation and decreased over time, and Wegovy’s says the same in substance. If a step goes badly, Wegovy’s SmPC explicitly allows delaying the increase or stepping back down until symptoms improve. Raise it with your doctor: it is a standard adjustment, not a failure.
Around weeks 16–20: the top of the curve. Wegovy’s titration is complete at 16 weeks (2.4 mg); Mounjaro’s continues depending on the target dose. The EMA’s assessment of the STEP trials places the peak around week 20: at that point, roughly 38% of semaglutide patients have a digestive effect on any given day.
After week 20: the decline. Frequency then drops markedly: by trial end (68 weeks), about 10% of patients still had nausea on a given day. And once a maintenance dose is tolerated, it tends to stay tolerated: in STEP 4, among 803 participants stabilized at 2.4 mg, there were only 2 discontinuations for digestive effects across the rest of the trial.
The official numbers, drug by drug
Wegovy (SmPC, STEP 1–4 trials, 68 weeks): nausea 43.9% (16.1% on placebo) · diarrhea 29.7% (15.9%) · vomiting 24.5% (6.3%) · constipation 24.2% (11.1%) · abdominal pain 19.7% (10.0%). Most events were mild to moderate in severity and of short duration, per the SmPC. Treatment discontinuation for digestive effects: 4.3%.
Mounjaro (SmPC, SURMOUNT-1 trial, 72 weeks): nausea 24.6% / 33.3% / 31.0% by dose (5 / 10 / 15 mg) versus 9.5% on placebo · diarrhea 18.7–23.0% · digestive effects mainly mild (60.8%) or moderate (34.6%) in severity. Discontinuation for digestive effects: 1.9–4.4% depending on dose.
Also common for both: reflux, burping, bloating, dizziness, hair loss, and injection-site reactions.
For the direct comparison between the two drugs (the SURMOUNT-5 trial), see our full Wegovy vs Mounjaro comparison.
Day-to-day management: what official sources say
- Adjust the climb: delaying a step or temporarily stepping down is provided for in the SmPC, a decision to make with your doctor.
- Drink a lot: both leaflets ask for it explicitly (it is important to avoid dehydration by drinking plenty of fluids), especially with vomiting or diarrhea. The UK’s NHS (Cambridge University Hospitals) puts a number on it: 2 to 3 liters of water or sugar-free drinks a day.
- On rough days, the same hospital advises: bland, low-fat foods (crackers, toast), small frequent portions, eating slowly, stopping when full, avoiding fried and fatty foods.
- For constipation: fiber, hydration, and regular activity: “even a daily walk” (NHS).
- If you take a sulfonylurea or insulin (diabetes): hypoglycemia risk rises: the SmPCs provide for reducing their dose at initiation; your doctor will adjust the doses.
When to seek help immediately
The official leaflets list warning signs that should not wait:
- Severe and persistent stomach pain, possibly radiating to the back: a possible sign of pancreas inflammation (pancreatitis, uncommon) → seek immediate medical help.
- Severe vomiting or diarrhea that prevents you from staying hydrated: risk of dehydration and downstream effects on the kidneys.
- Signs of a severe allergic reaction (rare): breathing difficulties, swelling of the face or throat, fast heartbeat → emergency care.
- Wegovy specifically: sudden painless vision loss in one eye (very rare) → see a doctor immediately; severe constipation with pain, bloating and vomiting.
And for any bothersome or unusual effect: talk to your doctor or pharmacist.
Logging your effects, day by day
One detail that transforms appointments: being able to say when nausea happens relative to your injections and dose changes. That is exactly what the Effects feature in the Doza app does: two taps after an injection to note how you feel (with optional intensity), and your journal places each effect at day +1, day +2… after your dose.
📱 Your effects, your weight, your doses: in one place. Doza keeps your journal in a few seconds a week, and your measurements and doses never leave your iPhone. 14-day free trial on the annual plan. Discover Doza →
FAQ — Wegovy and Mounjaro side effects
How long does the nausea last?
A single episode lasts a median of 8 days (Wegovy SmPC). Across the whole treatment, frequency peaks around week 20 then declines (semaglutide data, STEP trials). About 10% of patients still have nausea on a given day at 68 weeks.
Do the side effects eventually go away?
That is the leaflets’ own message: they usually go away over time (Wegovy) and decrease over time in most patients (Mounjaro). Constipation is the slowest to fade (median 47 days).
Which has more side effects, Wegovy or Mounjaro?
The profiles are very close, and rates from different trials cannot be compared directly. In the only head-to-head study, nausea was almost identical (about 44% on both sides); see our full Wegovy vs Mounjaro comparison, linked above.
Can the dose climb be slowed down if it goes badly?
Yes: the SmPC provides for delaying an increase or returning to the previous step until things improve. A decision to make with your doctor.
Does nausea come back after every injection?
Studies do not describe that pattern: at a stable dose, drug levels hold steady week to week. The sensitive windows are the dose steps, not each shot.
When should I worry?
Severe persistent stomach pain radiating to the back, inability to stay hydrated, signs of severe allergy, sudden vision change: seek care immediately (exact leaflet wording above).
Sources: Wegovy SmPC & leaflet and Mounjaro SmPC & leaflet (EMA, consulted 29 August 2026) · STEP 1, N Engl J Med 2021 (detail: ClinicalTrials.gov NCT03548935) · SURMOUNT-1, N Engl J Med 2022 · Wharton et al., Diabetes Obes Metab 2022 (GI-effect kinetics across STEP trials) · EMA public assessment report, Wegovy (peak around week 20) · NHS Cambridge University Hospitals (practical advice) · ameli.fr (follow-up, updated 12 June 2026) · head-to-head: SURMOUNT-5, ClinicalTrials.gov NCT05822830. Last updated: 29 August 2026. Published by Doza (INFINI CONSULTING) — a French GLP-1 tracking app.