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 Day 2 Side Effects and UK Access
Many people experience side effects on day 2 after their first Mounjaro injection. Common early symptoms include mild nausea, stomach discomfort, or fatigue as your body adjusts to the medication. In the UK, you can access tirzepatide (Mounjaro) through NHS specialist weight management services or via private online prescription. This guide covers what to expect on day 2, how side effects typically progress, and the cost and access routes available to UK adults.
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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.
Cost and Access Routes for Mounjaro in the UK
NHS access: Mounjaro is approved by NICE for use within NHS tier 3 specialist weight management services. Access is through referral from your GP to your local integrated care board (ICB) weight management team. However, NHS availability varies significantly by region, and waiting lists can extend several months to over a year in some areas. Not all ICBs currently fund tirzepatide, so eligibility depends on your location and local commissioning decisions.
Private prescription access: You can obtain a Mounjaro prescription privately through an online clinical consultation with a UK-licensed prescriber. If clinically appropriate following assessment, a prescription is issued and dispensed by a GPhC-registered pharmacy. Private Mounjaro costs typically range from £129 to £320+ per month depending on your dose (starting 2.5 mg through to maximum 15 mg). This route offers faster access without NHS referral — prescriptions can be issued within days.
Dose and costs: Your starting dose of 2.5 mg usually costs less than higher maintenance doses (5 mg, 10 mg, 15 mg). Many people budget £150–£250 monthly once they reach their therapeutic dose. Prices vary between private providers, so it's worth comparing before starting treatment.
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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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What Happens on Day 2 and the Online Assessment Process
On day 2 after your first 2.5 mg injection, side effects often peak as your body begins adjusting to the GLP-1 and GIP receptor agonist effects. You may notice nausea, reduced appetite, mild stomach pain, or fatigue. These symptoms typically subside within 3–7 days. If accessing Mounjaro privately, the online consultation process is straightforward: you'll complete a health questionnaire, have a brief video or phone call with a prescriber, and if approved, receive your prescription within 24–48 hours. The prescriber will discuss your dose titration plan — how your weekly dose increases from 2.5 mg up to 5 mg, 7.5 mg, and beyond over several weeks. Use our GLP-1 weight loss calculator to estimate potential results at your target dose, and track your progress with our free progress tracker once you begin 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.
What side effects are most common on day 2 of Mounjaro?
Nausea, stomach discomfort, reduced appetite, and fatigue are the most commonly reported side effects on day 2. These are expected as your body adjusts to the medication and typically resolve within a few days. Taking small, frequent meals and staying hydrated can help. If symptoms are severe or persistent, contact your prescriber.
How much does Mounjaro cost per month in the UK privately?
Private Mounjaro costs typically range from £129 to £320+ per month depending on your dose. Starting doses (2.5–5 mg) are usually cheaper than higher maintenance doses (10–15 mg). Prices vary between online prescription providers, so compare costs before committing. Some providers offer subscription discounts for regular orders.
Can I get Mounjaro on the NHS in the UK?
Yes, Mounjaro (tirzepatide) is approved by NICE for use within NHS tier 3 specialist weight management services. You'll need a GP referral to your local weight management team. However, availability varies by region and some areas have long waiting lists. Check with your GP about local NHS provision in your area.
How does the online prescription process work for Mounjaro?
You complete an online health questionnaire, then have a brief consultation (video or phone) with a UK-licensed prescriber. If clinically suitable, a prescription is issued and sent to a GPhC-registered pharmacy for dispensing. The whole process typically takes 24–48 hours. Your prescriber will discuss dose titration and side effect management before you start.
Is Mounjaro the same as Wegovy or tirzepatide?
Mounjaro is the brand name for tirzepatide. Wegovy is a different medication (semaglutide). Both are GLP-1 weight loss injections available in the UK, but Mounjaro is a dual GIP/GLP-1 agonist whilst Wegovy is GLP-1 only. Clinical trials show slightly different average weight loss outcomes between the two medications, though individual results vary significantly.
Ready to take control of your weight loss journey?
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