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
Mounjaro 2.5mg Side Effects — UK Cost and Access
Mounjaro (tirzepatide) is a prescription-only weight loss injection that starts at a 2.5mg dose. The starting dose typically causes fewer side effects than higher doses, though nausea and digestive changes are common. Understanding potential side effects, UK costs, and how to access Mounjaro through NHS or private prescription can help you make an informed decision about whether this treatment is right for you. Our free GLP-1 weight loss calculator can help you estimate potential results at different doses.
10,000+ calculations today · NHS-aligned thresholds · 100% free
Calculate Your BMI Instantly
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.
Mounjaro 2.5mg Side Effects and What to Expect
The 2.5mg starting dose of Mounjaro is designed to help your body adjust to tirzepatide with minimal disruption. Very common side effects affecting more than 1 in 10 people include nausea, diarrhoea, constipation, and mild stomach discomfort. Many people find these effects reduce after the first few weeks as their body adapts.
Less common but possible effects include vomiting, indigestion, headache, dizziness, fatigue, and injection site reactions like redness or bruising. Hair loss (alopecia) has been reported in some users. Serious side effects are rare but may include severe stomach pain suggesting pancreatitis, which requires immediate medical attention.
The 2.5mg dose is taken once weekly via the Mounjaro KwikPen. You'll stay on this dose for 4 weeks before your prescriber considers increasing to 5mg. Starting low allows your prescriber to monitor how well you tolerate tirzepatide before adjusting upwards.
Clinically BackedWeight Loss
No appointments. No waiting rooms. Just care — from a UK-regulated online pharmacy.
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.
Mounjaro Cost in the UK — NHS vs Private Access
NHS access: Tirzepatide (Mounjaro) is approved by NICE for use through NHS specialist weight management services. However, NHS availability varies significantly by region and waiting lists can be months or years. You'll need a GP referral to tier 3 or 4 specialist services, and access depends on your local Integrated Care Board (ICB) funding and availability.
Private prescription cost: Private prescriptions through online consultations typically cost between £129–£180 per month depending on dose and provider. The 2.5mg starting dose is usually at the lower end of this range. A private online consultation with a UK-licensed prescriber costs around £49–£99 and must be completed before any prescription is issued. No specific pharmacy names are recommended, but ensure you use a GPhC-registered pharmacy.
Accessing Mounjaro privately: You'll complete an online health questionnaire and consultation with a UK-licensed prescriber. If approved, your prescription is sent to a registered pharmacy for dispensing. The entire process typically takes 24–48 hours. Accessing via NHS: Ask your GP for a referral to your local specialist weight management service. You must have a BMI of 30 or above, or 27 or above with weight-related health conditions (type 2 diabetes, high blood pressure, sleep apnoea). NHS treatment is free once prescribed, but waiting times vary. Use our free BMI calculator to check your eligibility range, and discuss both routes with your GP.
- 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 are the most common side effects of Mounjaro 2.5mg?
Nausea, diarrhoea, constipation, and stomach pain are very common, affecting more than 1 in 10 people. These often improve within a few weeks as your body adjusts. Less common effects include vomiting, indigestion, headache, and fatigue. Serious side effects like severe stomach pain are rare but require immediate medical attention.
How much does Mounjaro 2.5mg cost in the UK?
Private prescription costs typically range from £129–£180 per month for the 2.5mg starting dose, plus an online consultation fee of £49–£99. NHS prescriptions are free once approved through specialist services, though waiting times vary by region. Prices vary between providers, so it's worth comparing before starting treatment.
Can I access Mounjaro 2.5mg through the NHS?
Yes, but only through specialist tier 3 or 4 weight management services. You need a GP referral and must meet eligibility criteria (BMI 30+ or 27+ with weight-related health conditions). Availability varies significantly by region—some areas have longer waiting lists than others. Discuss NHS access with your GP.
What happens after 4 weeks on Mounjaro 2.5mg?
After 4 weeks, your prescriber will assess your response and tolerance before considering an increase to 5mg. Dose escalation happens every 4 weeks until reaching an effective maintenance dose (usually 10–15mg), though you may stay on 2.5mg or 5mg if that's working well for you. Your prescriber monitors your progress throughout.
Is Mounjaro the same as Wegovy?
No. Both are GLP-1 weight loss injections licensed in the UK, but Mounjaro (tirzepatide) uses a dual GIP and GLP-1 mechanism, while Wegovy (semaglutide) is a GLP-1 agonist only. Mounjaro starts at 2.5mg; Wegovy starts at 0.25mg. Clinical trial data shows both support weight loss, though individual results vary. Your prescriber will help choose the right option for you.
Ready to take control of your weight loss journey?
Start with a free BMI check, explore your GLP-1 options, or begin tracking your progress today. No sign-up. No cost. Just results.