Managing Mounjaro and Wegovy Side Effects: A GP Clinical Guide

Mounjaro (tirzepatide) and Wegovy (semaglutide) are among the most effective weight loss medications available in the UK. For the majority of patients, the benefits of significant, sustained weight loss and improved metabolic health far outweigh the side effects. However, side effects are real, and managing them well is essential for staying on treatment long enough to achieve your goals.

This guide, written from a GP teams clinical perspective, explains the most common side effects and the evidence-based strategies we use at Calleva Clinic to help patients manage them.

Understanding Why Side Effects Happen

GLP-1 receptor agonists like Mounjaro and Wegovy work in part through the gut: they slow gastric emptying, reduce appetite via signals to the brain, and alter the digestive environment. Most side effects are a direct consequence of these mechanisms acting on a gut that hasn't yet adapted to the medication.

Importantly, side effects are typically dose dependent and time limited. They tend to peak in the first few weeks at each new dose and improve significantly as the body adjusts. This is why a gradual dose escalation protocol is clinically important and why patients who experience early side effects should be encouraged rather than deterred.

Nausea: The Most Common Side Effect

Nausea affects a significant proportion of patients when starting GLP-1 medication or increasing their dose. It is usually mild to moderate and tends to improve within one to two weeks at each dose level.

Evidence based strategies to reduce nausea:

• Eat smaller, more frequent meals rather than large portions

• Avoid fatty, greasy, or heavily spiced foods, particularly in the early weeks

• Eat slowly and chew food thoroughly

• Avoid lying down immediately after eating

• Stay well hydrated with small, regular sips of fluid

• Consider ginger in foods or drinks, which has evidence for reducing nausea

• Ask your clinical team about digestive enzyme support, which can ease the digestive burden

  
  

Constipation

Constipation is common on GLP-1 therapy because slowed gastric emptying means food spends longer in the digestive tract, and reduced food intake means less bulk to stimulate bowel movement.

• Increase fluid intake consistently throughout the day

• Prioritise dietary fibre from vegetables, fruit, and wholegrains (as tolerated)

• Maintain regular physical activity, which supports bowel motility

• Consider an osmotic laxative such as Movicol if dietary measures are insufficient

• Ask about magnesium supplementation, which can support bowel regularity

  
  

Fatigue

Some patients experience fatigue, particularly in the early weeks of treatment or following dose increases. This is often multifactorial: reduced calorie intake, possible nutritional deficiencies, and the body adapting to a changed metabolic state all contribute.

• Prioritise adequate protein intake to maintain energy and muscle function

• Ask your clinical team to check for nutritional deficiencies: particularly B12, vitamin D, iron, and magnesium

• Maintain sleep regularity and avoid severe calorie restriction

• Gentle exercise, even walking, supports energy levels and mood

  
  

Acid Reflux and Heartburn

Slowed gastric emptying can worsen reflux symptoms in some patients, particularly those with pre-existing reflux disease.

• Avoid eating within two to three hours of lying down

• Raise the head of your bed slightly if night-time symptoms are problematic

• Avoid known reflux triggers: caffeine, alcohol, carbonated drinks, and acidic foods

• Discuss with your GP if symptoms are persistent: acid suppressing medication may be appropriate

  
  

When to Contact Your Clinical Team

Most side effects are manageable and self limiting. However, you should contact Calleva Clinic promptly if you experience:

• Severe or persistent abdominal pain

• Vomiting that prevents you from keeping fluids down

• Signs of dehydration: dark urine, dizziness, or rapid heart rate

• Significant mood changes or any new or worsening mental health symptoms

Frequently Asked Questions

How long do Mounjaro side effects last? Most side effects are dose dependent and time limited. Nausea typically improves within one to two weeks at each dose level. If side effects are persistent or severe beyond this timeframe, your clinical team may recommend pausing dose escalation or adjusting your support protocol.

Are Mounjaro side effects worse than Wegovy? Both medications have similar side effect profiles as GLP-1 receptor agonists. Mounjaro also acts on GIP receptors, which may influence tolerability in some patients. Individual responses vary considerably, and what causes significant side effects in one person may be well tolerated by another.

Can I take anti sickness medication on Mounjaro or Wegovy? Some over the counter anti nausea medications such as cyclizine or domperidone may be appropriate in the short term. Always discuss with your prescribing clinician before adding any medication to manage side effects, as interactions and contraindications need to be considered.

Should I reduce my dose if side effects are severe? If side effects are significantly affecting your quality of life, a temporary dose reduction or delayed escalation is preferable to stopping treatment altogether. Your Calleva Clinic clinical team can guide you through this: do not adjust your dose without clinical advice.

Ready to start your weight loss journey with expert clinical support? Calleva Clinic offers free consultations with our GP-led team. We prescribe Mounjaro (tirzepatide) and Wegovy (semaglutide) with personalised support, home delivery, and ongoing clinical monitoring across England. Visit: www.callevaclinic.co.uk/weight-loss-injections