CommonNausea, diarrhoea, vomiting, constipation and abdominal discomfort
Common effects, warning signs and the right response
Wegovy and Mounjaro side effects
Digestive symptoms are common, especially when treatment starts or the dose changes. Most are manageable, but persistent symptoms should be reviewed and a small number of warning signs need urgent medical attention.
ReviewDiscuss persistent symptoms before increasing the dose
EmergencyCall 112 for breathing difficulty, collapse or rapid facial or throat swelling
Understanding frequency and severity
Common symptoms or urgent warning signs?
“Very common” is a formal leaflet category meaning at least 1 in 10 people. “Uncommon” means at least 1 in 1,000 but fewer than 1 in 100. Individual trial percentages differ, so figures from Wegovy and Mounjaro studies should not be directly compared.
Usually manageable
Common side effects
Very common · at least 1 in 10
- Nausea or reduced appetite
- Diarrhoea or vomiting
- Constipation
- Abdominal pain or discomfort
- Indigestion, reflux, bloating or belching
- Headache or fatigue can also occur
43.9%Nausea
29.7%Diarrhoea
24.5%Vomiting
24.2%Constipation
Wegovy adult trials over 68 weeks. Mounjaro’s leaflet also classifies these digestive effects as very common in weight-management trials, but its percentages come from different studies.
What to do
Record the symptom, injection date, dose, fluid intake and urine output. Contact the doctor if it persists or interferes with normal activity. The plan may include practical advice, suitable symptom relief, delaying an increase or changing treatment.
Do not wait
More serious warning signs
Acute pancreatitis · uncommon
Severe, persistent abdominal pain—sometimes travelling through to the back—with or without repeated vomiting requires prompt assessment.
Severe allergic reaction · rare
Breathing difficulty, rapid swelling of the face, lips, tongue or throat, voice change, widespread hives or itching, marked light-headedness or collapse.
Severe dehydration or bowel warning signs
Repeated vomiting, inability to keep fluids down, very little urine, confusion, severe constipation with swelling or vomiting, or inability to pass stool or wind.
What to do
Call 112 immediately for breathing difficulty, rapid facial or throat swelling, collapse or another life-threatening reaction. Seek urgent medical assessment for severe persistent abdominal pain, repeated vomiting or signs of significant dehydration.
Notice the pattern
Record when the symptom began, the latest injection date and dose, food and fluid intake, bowel movements, urine output and whether the symptom is improving or becoming more intense.
Speak with the prescribing doctor
Persistent nausea, repeated vomiting, ongoing diarrhoea, troublesome constipation or symptoms that limit normal activity should be reviewed. Do not increase the dose simply because the calendar says it is time.
Use urgent care when necessary
Severe symptoms are not managed by waiting for a routine follow-up. Contact urgent medical services, or call 112 when symptoms could be life-threatening.
!
Safety first
Do not increase through persistent symptoms
GLP-1 dose escalation is conditional on tolerability. A dose may need to stay unchanged for longer, be paused, reduced or changed after clinical review. Never try to hide serious symptoms simply to continue treatment.
Call 112 for a life-threatening emergency.
Common questions
Side effects and when to contact a doctor
Are side effects worse after a dose increase?
They can be. Digestive effects are often noticed after starting treatment or increasing a dose, so tolerability should be reviewed before another increase.
What can help with nausea?
Small meals, eating slowly, avoiding very rich foods and maintaining fluids may help. Persistent nausea should be discussed with the prescribing doctor.
Should I stop immediately if I have side effects?
Do not change the dose on your own for mild symptoms. Contact the prescribing team. Stop and seek urgent help for a suspected severe allergic reaction or other serious warning signs.
When is vomiting urgent?
Seek urgent medical advice for repeated vomiting, inability to keep fluids down, very little urine, marked dizziness, confusion or severe abdominal pain.
Can constipation become serious?
Yes. Severe pain, marked swelling, vomiting, or inability to pass stool or wind requires urgent assessment.
Does every abdominal pain mean pancreatitis?
No. Mild digestive discomfort is common, but severe and persistent pain, particularly if it travels to the back or occurs with vomiting, requires prompt assessment.
Can a doctor prescribe treatment for side effects?
Depending on the symptom and clinical assessment, a doctor may recommend practical measures, prescribe suitable symptom relief, delay an increase or change the treatment plan.
Should my dose increase while symptoms continue?
Dose escalation should not be automatic. Persistent or troublesome symptoms should be reviewed before moving to a higher dose.
Clinical sources: EMA — Wegovy product information · EMA — Mounjaro product information. Frequency bands and figures reflect the current official product information. This general guide does not replace an individual consultation.
Medically reviewed
Dr Ben Harry Clegg
General practitioner · Málaga registration 292911940 · Nerja Medical Center NICA 55712
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