Weight Medication Side Effects & When to Seek Help
What to expect with Wegovy (semaglutide) and Mounjaro (tirzepatide), and which symptoms need urgent attention
About These Medications
Wegovy (semaglutide) and Mounjaro (tirzepatide) are GLP-1 receptor agonist medications prescribed for chronic weight management. They work by acting on gut hormones to regulate appetite and slow gastric emptying. Both are given as once-weekly subcutaneous injections.
Like all medications, they can cause side effects. Most are related to the digestive system and tend to lessen as your body adjusts during the dose escalation period.
Common Side Effects (Usually Improve Over Time)
The following side effects are reported by many people starting GLP-1 medications. They are most common during the early weeks of treatment or after each dose increase, and typically improve with time.
Gastrointestinal discomfort
Nausea, constipation, diarrhoea, burping, and bloating are commonly reported, particularly in the early weeks of treatment. These effects are related to how GLP-1 medications slow digestion and typically improve as your body adjusts.
Reduced appetite
A significant reduction in hunger and food interest is an expected effect of these medications. Ensure you are still consuming adequate nutrition — speak to your doctor if you find it very difficult to eat.
Injection site reactions
Mild redness, itching, bruising, or a small lump at the injection site. These are common and usually resolve within a day or two. Rotating injection sites each week helps prevent this.
Headaches
Some people experience headaches in the early weeks of treatment. Ensure adequate fluid intake. Report severe or persistent headaches to your doctor.
Fatigue
Tiredness can occur, particularly early in treatment or after a dose increase. Usually settles within a few days to weeks.
Mood changes
Some people notice changes in mood or energy. Report persistent low mood, anxiety, or any thoughts of self-harm to your doctor promptly.
💡 Side effects and dose increases
Side effects are most noticeable in the first few weeks of a new dose. Doses are increased gradually for this reason. If side effects are significantly affecting your quality of life, speak to your doctor before the next scheduled increase — it may be appropriate to stay at your current dose for longer.
Symptoms to Discuss With Your Doctor (Non-Urgent)
These symptoms do not need emergency care but should be discussed with your prescribing doctor within a few days:
Digestive side effects that are persistent and affecting your ability to eat, drink, or function normally
Injection site reactions that are spreading, warm to touch, or not resolving
Significant hair thinning (can occur with rapid weight loss — usually temporary)
Persistent low mood, anxiety, or changes in mental health
Any side effect that is significantly affecting your daily life or willingness to continue treatment
Emergency Red-Flag Symptoms
The following symptoms require immediate emergency care. Stop the medication and call 000 or go directly to your nearest Emergency Department:
🚨 Call 000 or go to Emergency for
- Severe abdominal pain — particularly if it is persistent, intense, or radiating to the back. This may indicate pancreatitis, which is a serious but rare side effect of GLP-1 medications. Stop your medication and seek emergency care immediately.
- Right upper abdominal pain with jaundice or fever — GLP-1 medications are associated with an increased risk of gallstones and gallbladder disease. Severe right-sided abdominal pain, particularly with yellowing of the skin or eyes (jaundice), requires emergency assessment.
- Rapid or sustained increase in heart rate — a resting heart rate consistently more than 15–20 beats per minute above your usual rate, especially if accompanied by chest discomfort or palpitations, should be assessed urgently.
- Signs of serious allergic reaction — swelling of the face, lips, throat, or tongue; difficulty breathing or swallowing; hives; or feeling faint after injection. Call 000 immediately.
- Sudden changes in vision — blurring, distortion, or loss of vision in one or both eyes. This can be related to rapid changes in blood sugar levels and requires prompt assessment by a doctor.
- Neck lump or difficulty swallowing — a new lump in the neck, difficulty swallowing, or hoarse voice may rarely indicate thyroid effects. These require medical assessment.
⚠️ If you vomit or cannot take fluids\
If you are vomiting repeatedly and cannot keep fluids down, seek medical advice promptly. This is not an emergency unless you are severely unwell, but dehydration can develop quickly and you may need review or intravenous fluids.
📞 In an emergency
Emergency: Call 000
After-hours health advice: 1800 022 222 — healthdirect Australia (24/7 nurse-on-call helpline)
For non-urgent questions about your treatment, contact your prescribing doctor's clinic during business hours.
Visual Quick Reference
Weight management medication side effects — see the Arami resource guide
Concerned about a side effect?
Book a review appointment to discuss any concerns about your weight management treatment.
Medical Disclaimer
This list is not exhaustive. Always read the Consumer Medicines Information (CMI) and Instructions for Use leaflet supplied with your medication for the complete list of possible side effects. If you are ever unsure whether a symptom is serious, seek medical advice promptly — it is always better to be assessed.