The UK's most complete GLP-1 guide
Every Question Answered. Every Side Effect Explained.
- How GLP-1 medications work
- Mounjaro vs Wegovy compared
- Injection instructions
- Side effects & solutions
- What to eat on treatment
- FAQs answered
Free tracker included with every download this week
What Are the Symptoms of Mounjaro?
Mounjaro (tirzepatide) is a prescription-only weight management injection that may cause side effects as your body adjusts to the medication. Most symptoms are mild and tend to improve over time, particularly as your body adapts to each dose increase. Understanding what to expect can help you manage the adjustment period and decide whether this treatment is right for you. This guide covers the most common symptoms reported in clinical trials and how they typically progress during treatment.
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Enter your height and weight below. Supports both imperial (stone & lbs) and metric (kg). Results include NHS category, healthy weight range, and ethnicity adjustments.
What Is BMI and Why Does It Matter?
Body Mass Index (BMI) is the most widely used screening tool for assessing whether your weight falls within a healthy range. Used by the NHS, GPs, and weight management services across the UK, BMI provides a quick snapshot of your weight relative to your height. The formula is simple: your weight in kilograms divided by your height in metres squared (kg/m²).
While BMI isn't a perfect measure — it doesn't account for muscle mass, bone density, or fat distribution — it remains the standard first step in identifying potential weight-related health risks including type 2 diabetes, cardiovascular disease, high blood pressure, and certain cancers.
The NHS also recommends adjusted thresholds for people of South Asian, Chinese, or Black African heritage — a BMI of 23 or above is classified as overweight, and 27.5 as obese. Our calculator includes this adjustment as a one-click toggle.
Common Mounjaro Symptoms and Side Effects
The most frequently reported symptoms of Mounjaro occur in the gastrointestinal system. Nausea is the most common, affecting more than 1 in 10 people, particularly in the first few weeks of treatment or after a dose increase. Diarrhoea and constipation are also very common, along with stomach pain and indigestion. Many patients experience reduced appetite, which is actually the intended mechanism of the tirzepatide medication — it signals to your brain that you feel fuller, so you naturally eat less.
- Nausea — usually improves within a few days to weeks
- Diarrhoea or constipation — digestive adjustment phase
- Stomach (abdominal) pain — mild to moderate discomfort
- Vomiting — less common but can occur
- Indigestion and acid reflux — particularly after meals
- Loss of appetite — expected and desired effect
- Fatigue and dizziness — typically mild and temporary
These symptoms occur because tirzepatide slows how quickly food moves through your stomach and alters hunger hormones. Most people find symptoms settle after the first one to two weeks on a new dose.
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How It Works
Three simple steps to understand your weight and take action.
Enter your height and weight in our free calculator. Get your BMI, NHS category, healthy weight range, and ethnicity-adjusted thresholds instantly.
If your BMI suggests you're overweight or obese, explore our GLP-1 calculators to project potential weight loss on Mounjaro or Wegovy.
Use our progress tracker to log your weight weekly, visualise your journey with charts, and stay motivated — all stored privately in your browser.
Free Weight Loss Tools & Guides
Everything you need to understand your weight, explore medication options, and track your progress — completely free.
When to Seek Medical Help
Whilst most Mounjaro symptoms are mild and resolve on their own, some symptoms warrant urgent attention. Seek immediate medical help if you experience severe stomach pain that spreads to your back (possible pancreatitis), serious allergic reactions like swelling of the face, lips, or throat, or persistent vomiting lasting more than a few hours. Contact your GP if symptoms don't improve after two weeks on a dose, if you develop new symptoms not listed in the patient information, or if you're struggling to manage side effects. Your prescriber may adjust your dose or suggest strategies to reduce discomfort. Track your symptoms and any concerns using our free progress tracker to help you discuss them with your healthcare provider.
- Dual GIP/GLP-1 receptor agonist
- Up to 22.5% body weight loss (SURMOUNT-1)
- Weekly injection, dose escalation over 20+ weeks
- Available via private prescription in the UK
- Doses: 2.5mg → 5mg → 7.5mg → 10mg → 12.5mg → 15mg
- GLP-1 receptor agonist
- Up to 15–17% body weight loss (STEP trials)
- Weekly injection, 5-step dose escalation
- NHS & private prescription available
- Doses: 0.25mg → 0.5mg → 1mg → 1.7mg → 2.4mg
Mounjaro vs Wegovy: Head-to-Head
A side-by-side comparison of the two most popular GLP-1 weight loss medications available in the UK.
| Feature | Mounjaro | Wegovy |
|---|---|---|
| Drug class | Dual GIP/GLP-1 agonist | GLP-1 agonist |
| Active ingredient | Tirzepatide | Semaglutide |
| Avg. weight loss | 15–22.5% | 12–17% |
| Key trial | SURMOUNT-1 (2022) | STEP 1 (2021) |
| Max dose | 15 mg weekly | 2.4 mg weekly |
| Escalation period | 20–32 weeks | 16–20 weeks |
| Administration | Weekly injection (pen) | Weekly injection (pen) |
| NHS availability | Private prescription only | NHS & private |
| Approx. private cost | £150–£250/month | £150–£300/month |
| Common side effects | Nausea, diarrhoea, constipation | Nausea, vomiting, diarrhoea |
Data sourced from SURMOUNT-1 and STEP 1 clinical trials. Costs are approximate and vary by provider. Always consult a prescriber.
Am I Eligible for Weight Loss Medication?
In the UK, eligibility for GLP-1 weight loss medications like Mounjaro and Wegovy is based on your BMI and overall health profile.
- BMI of 30 or above (obese)
- Age 18 or over
- No contraindicated conditions
- Committed to lifestyle changes
- BMI of 27 or above
- Plus type 2 diabetes
- Or high blood pressure
- Or obstructive sleep apnoea
Use our BMI calculator to check whether your BMI falls within the eligible range.
How We Built These Tools
Every calculator and guide on myweightcheck is built with accuracy and transparency in mind. Our BMI calculator uses the standard WHO formula with NHS-aligned category thresholds. Our GLP-1 projections are modelled on published clinical trial data from SURMOUNT and STEP studies.
All data stays on your device. We don't require sign-ups, and we don't store your health information on any server. Your progress tracker saves data locally in your browser using localStorage, so only you can see it.
We're based in the UK and our tools are designed specifically for UK users — supporting stone & lbs by default, referencing NHS guidelines, using NICE-approved medication data, and linking to GPhC-registered pharmacies.
Frequently Asked Questions
Common questions about BMI, weight loss medications, and our free UK tools.
How long do Mounjaro symptoms last?
Most common symptoms improve within 2–7 days of starting or increasing your dose. Nausea and digestive changes typically settle as your body adapts. If symptoms persist beyond two weeks, contact your GP — they may adjust your dose or provide additional support strategies.
Can I reduce nausea from Mounjaro?
Yes. Eat smaller, more frequent meals; avoid fatty or greasy foods; stay hydrated; eat slowly; and avoid sudden movements. Some people find ginger tea or anti-nausea medication helpful. Discuss options with your GP or pharmacist if nausea is severe.
Is the reduced appetite a side effect or the intended effect?
It's the intended effect. Tirzepatide works by activating GLP-1 receptors in the brain that regulate appetite and fullness. Feeling less hungry is how the medication supports weight loss — not a harmful side effect, but the mechanism of action.
Does Mounjaro cause hair loss?
Hair loss (alopecia) is reported as a common side effect in some patients, though it's less frequent than nausea or digestive changes. It's usually temporary and relates to gradual weight management. Discuss persistent hair loss with your GP — adequate protein intake and micronutrient levels may help.
How does Mounjaro compare to Wegovy side effects?
Both medications are GLP-1-based (Mounjaro is dual GIP+GLP-1). Side effects are similar — nausea, diarrhoea, constipation — but Mounjaro may have slightly different tolerability due to its dual mechanism. Individual responses vary significantly; your prescriber can advise which suits you better. ```
Ready to take control of your weight loss journey?
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