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
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Mounjaro Side Effects at 5mg — What to Expect in the UK
The 5mg dose of Mounjaro (tirzepatide) is typically the first maintenance dose after a four-week starting phase. Most side effects are gastrointestinal and often improve as your body adjusts. Understanding what to expect at the 5mg dose can help you manage your weight loss journey more effectively. This UK health guide covers the most common side effects reported in clinical trials, how long they typically last, and when you should contact your GP for support.
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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.
Most Common Side Effects at 5mg Mounjaro
At the 5mg dose, clinical trials showed that the most frequently reported side effects are nausea, diarrhoea, vomiting, and constipation. These gastrointestinal effects occur because tirzepatide slows how quickly food moves through your stomach. The good news is that many people find these symptoms improve significantly within the first two to four weeks as their body adjusts to the medication. Nausea is typically the most common side effect at 5mg, affecting up to 1 in 10 users, whilst diarrhoea and constipation may alternate as your digestive system adapts. Other side effects at this dose may include indigestion, stomach pain, and loss of appetite. Most side effects are mild to moderate in severity. If you experience severe or persistent symptoms, always contact your GP or prescriber for guidance rather than stopping the medication yourself.
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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.
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Managing 5mg Side Effects and When to Seek Help
To manage nausea and gastrointestinal symptoms at 5mg, eat smaller meals more slowly, avoid greasy or spicy foods, and stay well hydrated. Ginger tea, ginger biscuits, or prescribed anti-nausea medication may help. Most side effects settle within weeks, but contact your GP immediately if you develop severe stomach pain spreading to your back (possible pancreatitis), serious allergic reactions, or persistent vomiting lasting more than a few hours. Your prescriber can adjust your dose or provide additional support. Use our free BMI calculator to monitor your health progress, and our GLP-1 weight loss calculator can help you understand realistic expectations at the 5mg dose alongside your lifestyle changes.
- 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 5mg side effects usually last?
Most gastrointestinal side effects peak in the first week or two and improve significantly within 2–4 weeks as your body adapts. Nausea may persist longer in some people but typically becomes manageable. Always allow 4 weeks before increasing your dose to give your body time to adjust.
Is nausea at 5mg normal with Mounjaro in the UK?
Yes, nausea is very common at 5mg—clinical trials showed it affected around 1 in 10 users. It's a sign the medication is working. Eating smaller meals, staying hydrated, and avoiding greasy foods usually helps. If nausea is severe, contact your prescriber.
Can I stop Mounjaro if side effects are too much?
Do not stop your medication without speaking to your prescriber first. They can provide support strategies, adjust your dose, or prescribe anti-nausea medication. Most people find side effects improve within weeks, but your GP or prescriber can help you manage them safely.
What side effects at 5mg mean I should contact my GP?
Contact your GP immediately for severe stomach pain spreading to your back, serious allergic reactions (swelling of face or throat), persistent vomiting, or any symptom that concerns you. Minor nausea and diarrhoea are normal, but severe symptoms need medical attention.
Is the 5mg dose of Mounjaro the same as Wegovy?
No—Mounjaro 5mg is roughly equivalent to Wegovy 0.5mg, but they are different medications. Mounjaro uses tirzepatide (dual GIP + GLP-1), whilst Wegovy uses semaglutide (GLP-1 only). Side effect profiles are similar but not identical. Your prescriber will choose the right medication for you.
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