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 5mg Side Effects & UK Access Guide
Mounjaro (tirzepatide) 5mg is the first maintenance dose after the starting dose, and understanding both its side effects and how to access it in the UK is important when considering this prescription-only weight management injection. This guide covers what happens at the 5mg dose, the most common side effects you might experience, and your options for obtaining Mounjaro through the NHS or private prescription routes in the UK.
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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 Side Effects at the 5mg Dose
At the 5mg maintenance dose, Mounjaro's most frequently reported side effects are gastrointestinal, particularly in the first few weeks as your body adjusts. Nausea affects many users initially but often improves over time as tolerance develops. Diarrhoea and constipation are also common — some people experience both at different times during their treatment cycle.
- Very common (more than 1 in 10 people): nausea, diarrhoea, vomiting, constipation, stomach pain
- Common (up to 1 in 10): indigestion, acid reflux, injection site reactions, fatigue, dizziness, hair loss
- Timing: Most GI side effects peak in weeks 1–4 after a dose increase and typically settle within 1–2 weeks
The 5mg dose represents the first step up from the starting 2.5mg dose. Many people find side effects are milder at 5mg than at higher doses like 10mg or 15mg. Your prescriber may keep you at 5mg for longer if you're managing well and seeing good results, rather than escalating further.
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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.
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Accessing Mounjaro in the UK: NHS vs Private Routes
NHS access: Mounjaro is available through NHS specialist tier 3 weight management services following NICE approval, but availability varies significantly by region. Waiting lists can extend several months, and eligibility typically requires a GP referral and a BMI of 30 or above (or 27+ with weight-related health conditions). Use our free BMI calculator to check your starting point.
Private access: You can obtain a Mounjaro prescription through UK-licensed online prescribers without an NHS referral. An online consultation costs £30–£50, and treatment typically costs £150–£250 per month depending on your dose. This route is faster (1–2 weeks from consultation to first injection) but is not funded by the NHS.
What to expect: Whether NHS or private, you'll need a clinical assessment confirming eligibility, baseline health checks, and ongoing monitoring while on treatment.
- 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.
Is Mounjaro 5mg a starting dose or a maintenance dose?
Mounjaro 5mg is the first maintenance dose. You start at 2.5mg for 4 weeks, then increase to 5mg in week 5. Most people continue at 5mg for at least 4 weeks before potentially escalating to 7.5mg or higher, depending on tolerability and weight loss response.
How much does Mounjaro 5mg cost privately in the UK?
Private Mounjaro 5mg typically costs £150–£180 per month through UK online prescribers. A KwikPen containing 4 weeks of 5mg doses (one injection per week) is the standard supply. Prices vary slightly between providers but do not vary significantly by dose at the lower maintenance levels.
Can I switch from Wegovy to Mounjaro on the NHS?
NHS switching between weight loss medications is not routine and depends on your local ICB (Integrated Care Board) policy. Both medications are available through NHS specialist services, but you cannot typically switch without specialist review. Private prescribers may support switching more readily.
What should I do if I experience severe side effects at 5mg?
Contact your prescriber immediately. Severe stomach pain, persistent vomiting, serious allergic reactions, or chest pain warrant urgent medical attention. Milder side effects (nausea, diarrhoea) often settle within 1–2 weeks — your prescriber may recommend dietary adjustments or staying at 5mg longer before escalating.
How do I check if I'm eligible for Mounjaro on the NHS?
Check your BMI using our free BMI calculator on this page. You're typically eligible for NHS consideration if your BMI is 30 or above, or 27–29.9 with a weight-related health condition (diabetes, high blood pressure, sleep apnoea, cardiovascular disease). Ask your GP about referral to tier 3 weight management services in your area.
Ready to take control of your weight loss journey?
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