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 Starter Kit: Everything You Need to Know
Starting Mounjaro (tirzepatide) is a significant step in your weight management journey. A Mounjaro starter kit includes your first KwikPen, injection supplies, and essential information about doses, storage, and administration. This guide covers everything UK adults need to know before beginning treatment, from understanding the 2.5 mg starting dose to managing common early side effects. Our GLP-1 weight loss calculator can help you project potential outcomes, while our BMI calculator provides personalised health context for your weight management goals.
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.
What Comes in a Mounjaro Starter Kit
A typical Mounjaro starter kit includes:
- One pre-filled KwikPen containing 2.5 mg (your first injection)
- Detailed patient information leaflet (PIL) with safety data and side effects
- Instructions on how to inject using the KwikPen device
- Guidance on storage and injection site rotation
- Emergency contact information and support resources
The KwikPen is a simple, pre-filled auto-injection device you use once per week. Each pen contains four doses (four weeks' supply). Your prescriber will provide clear instructions, and many online pharmacies include injection technique videos. You'll also receive information about what to do if you miss a dose or experience side effects. Keep all packaging and the patient information leaflet for reference — you may need to check dosing or storage guidance.
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.
Getting Started: The First Four Weeks
You'll start with a 2.5 mg dose for weeks 1–4, injected once per week on the same day. This is deliberately low to allow your body to adjust. Most people experience minimal side effects at this dose, though some may notice mild nausea or reduced appetite. Store your KwikPen in the fridge at 2–8°C until use. On injection day, you can remove it from the fridge 15–30 minutes before injecting — it doesn't need to be cold. Inject into your stomach, thigh, or upper arm, rotating sites each week. After four weeks, your prescriber will assess your progress and may increase your dose to 5 mg. Use our progress tracker to log your weekly weight and how you're feeling — this helps identify patterns and informs future dose adjustments.
- 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 do I store my Mounjaro KwikPen before using it?
Store unopened pens in the fridge at 2–8°C in the original carton. Do not freeze. Keep away from light and direct heat. Once you start using a pen, you can keep it at room temperature (below 30°C) for up to 30 days. Discard any pen 30 days after first use, even if it contains unused doses.
What's the difference between Mounjaro and Wegovy for starting treatment?
Both are once-weekly injections for weight management in the UK. Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist with a starting dose of 2.5 mg. Wegovy (semaglutide) is a GLP-1 agonist with a starting dose of 0.25 mg. Clinical trials showed Mounjaro achieved slightly higher average weight loss (~20.9% at maximum dose) compared to Wegovy (~14.9%), but individual results vary considerably.
What side effects should I expect in the first week?
Common early side effects include mild nausea, reduced appetite, and occasional indigestion. These typically decrease after a few days as your body adjusts. Drink plenty of water, eat small, frequent meals, and avoid greasy foods. If nausea is severe or doesn't improve within a few days, contact your prescriber. Serious side effects like severe stomach pain are rare but require immediate medical attention.
Can I take Mounjaro if I'm also taking diabetes medication?
If you're taking insulin or sulphonylureas for diabetes, your prescriber may need to adjust these doses as Mounjaro helps regulate blood sugar. Never stop or change diabetes medication without speaking to your GP or prescriber. Always inform your healthcare provider of all medications you're taking before starting Mounjaro.
What should I do if I miss my weekly injection?
If you miss your dose, inject within 4 days of the scheduled time and continue your normal schedule the following week. If more than 4 days have passed, skip that dose and take your next injection on the regular scheduled day. Never double-dose. Maintain at least 72 hours between injections. ```
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.