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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How to Get 2.5mg From a 5mg Mounjaro Pen
A 5mg Mounjaro KwikPen contains a single 5mg dose and cannot be split or divided to extract a 2.5mg dose. If you need a 2.5mg starting dose, your prescriber will issue a separate 2.5mg pen. This guide explains Mounjaro dose titration in the UK, how pens are designed, and what to do if you need a lower dose. Mounjaro (tirzepatide) is a prescription-only weight management injection, and your prescriber will select the correct starting dose for your clinical assessment.
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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.
How Mounjaro Pens Are Designed and Dosed
Each Mounjaro KwikPen contains exactly one pre-filled dose and is designed to deliver that dose in full — it cannot be partially used or divided. The available strengths are 2.5mg, 5mg, 7.5mg, 10mg, 12.5mg, and 15mg. Each pen delivers its full contents in a single weekly injection.
If you're prescribed a 2.5mg starting dose, you'll receive a 2.5mg pen, not a 5mg pen that you divide. Mounjaro's dose titration schedule involves increasing by 2.5mg every four weeks, so most patients start at 2.5mg and progress through standard increments.
- 2.5mg pens are used for weeks 1–4 (starting phase)
- 5mg pens are typically used for weeks 5–8 (first maintenance dose)
- Doses increase in 2.5mg increments if needed
- Never attempt to use half a pen or share a dose
Your prescriber selects your starting dose based on your health assessment, BMI, weight-related conditions, and whether you've taken similar medications before.
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.
NHS vs Private Prescribing and Dose Access in the UK
In the UK, Mounjaro is available through both NHS specialist weight management services and private online prescribers. Your access route affects which doses are available and how quickly you can start.
NHS route: Prescribed through tier 3 or tier 4 weight management services following GP referral. Your dose is selected and monitored by specialists. Availability and wait times vary significantly by region.
Private route: Prescribed by a UK-licensed prescriber following an online clinical assessment. A GPhC-registered pharmacy dispenses the prescription. Your prescriber will issue the correct starting dose pen for your circumstances — typically 2.5mg if you're new to GLP-1 medications like tirzepatide. Try our free GLP-1 weight loss calculator to estimate potential results at different doses and discuss outcomes with your prescriber.
Online prescription process: Complete a health questionnaire, a prescriber reviews your details within hours, and if approved, your prescription is sent to a pharmacy. Never attempt to obtain higher doses than prescribed or use doses designed for someone else. Your prescriber will guide your dose titration schedule — typically increasing by 2.5mg every four weeks if needed and tolerated. If you experience side effects on your current dose, contact your prescriber before your next injection rather than skipping doses or adjusting yourself.
- 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.
Can I use half a Mounjaro 5mg pen to get 2.5mg?
No. Mounjaro KwikPens are pre-filled with a single dose that cannot be split or divided. Each pen is sealed and delivers its entire contents. If you need 2.5mg, you must be prescribed a separate 2.5mg pen. Never attempt to partially use a pen — it compromises sterility and dose accuracy.
What if I've been prescribed the wrong Mounjaro dose?
Contact your prescriber immediately — do not attempt to adjust the dose yourself. If you received a 5mg pen but need 2.5mg, your prescriber can cancel that prescription and issue a 2.5mg pen instead. If side effects are severe, speak to your GP or prescriber before your next injection.
How does Mounjaro dose titration work in the UK?
Most patients start at 2.5mg once weekly for four weeks, then increase to 5mg for weeks 5–8. The dose increases by 2.5mg every four weeks thereafter if needed, up to a maximum of 15mg. Your prescriber controls this schedule based on your tolerance and response.
What's the difference between Mounjaro and Wegovy dose schedules?
Mounjaro starts at 2.5mg and increases by 2.5mg increments. Wegovy (semaglutide) starts at 0.25mg and increases more gradually through 0.5mg, 1mg, 1.7mg, and 2.4mg. Both are once-weekly injections, but Mounjaro uses higher absolute doses and a different titration pattern.
Where can I get a Mounjaro prescription in the UK?
Through NHS specialist weight management services (via GP referral, regional availability varies) or private UK-licensed prescribers (following online clinical assessment). Both routes require a prescription from a qualified prescriber. Never attempt to use someone else's Mounjaro pen or obtain doses without clinical assessment.
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.