Independent UK medicine guidance
Mounjaro fatigue and tiredness
Feeling tired or fatigued is listed as a common Mounjaro side effect, meaning it may affect up to 1 in 10 people. Some people notice tiredness after their injection or following a dose increase. However, fatigue has many possible causes and should not automatically be blamed on Mounjaro.
Why might you feel tired?
Possible explanations include:
- Your body adjusting to treatment
- Eating substantially less than before
- Not drinking enough
- Vomiting or diarrhoea
- Low blood pressure
- Poor sleep
- Low blood sugar, particularly with insulin or a sulphonylurea
- Iron, vitamin B12 or folate deficiency
- Thyroid problems
- Another illness or infection
Mounjaro may greatly reduce appetite. While this is part of its intended effect, eating very little can leave you short of energy and important nutrients.
What can you do?
Try to maintain regular, balanced meals even if the portions are smaller. Include a source of protein and some carbohydrate, particularly if you are active.
Drink regularly and look for signs of dehydration, including dark urine, dry mouth, headaches and dizziness on standing.
Increase activity gradually. A gentle walk may help with mild sluggishness, but persistent exhaustion is not something you should try to exercise through.
If tiredness began after a dose increase, tell your prescriber before taking the next higher dose. Dose escalation should depend on tolerability as well as weight loss.
Could it be low blood sugar?
Mounjaro alone has a relatively low risk of causing hypoglycaemia. The risk is considerably higher when it is combined with insulin or a sulphonylurea such as gliclazide.
Low blood sugar may cause:
- Sweating
- Shaking
- Hunger
- Dizziness
- Weakness or drowsiness
- A fast heartbeat
- Confusion or irritability
Follow your agreed hypo treatment plan and discuss repeated episodes with your diabetes team. Your other diabetes medication may need reviewing.
When should you contact a healthcare professional?
Speak to your GP or prescriber if fatigue is persistent, severe, worsening or interfering with normal life.
Seek more urgent help if fatigue comes with chest pain, breathlessness, fainting, confusion, black stools, persistent vomiting or severe abdominal pain.
Do not assume that profound fatigue is simply the price of losing weight.
Related Monj guides
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