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
How Long Does Mounjaro Take to Work After First Injection?
Most people notice early signs of Mounjaro working within the first 2–3 weeks after their first 2.5 mg injection, though full effects typically develop over 8–12 weeks as doses are increased. The medication begins affecting appetite and blood sugar regulation immediately, but weight loss becomes more noticeable once you reach maintenance doses (usually 5 mg or higher). Individual timelines vary considerably — some people feel differences within days, while others take several weeks. Access to Mounjaro in the UK depends on your route: NHS specialist services or private prescription through a GPhC-registered pharmacy. Understanding both cost and access options helps you plan realistically.
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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.
Mounjaro Private Prescription Costs by Dose in the UK
Private prescription costs for Mounjaro vary significantly depending on the dose and pharmacy. As a weekly weight loss injection, Mounjaro is dispensed in 4-week supplies (4 pre-filled KwikPens):
- 2.5 mg (starting dose): approximately £129–£179 per month
- 5 mg (first maintenance): approximately £149–£199 per month
- 7.5–10 mg (escalation): approximately £179–£229 per month
- 12.5–15 mg (maximum dose): approximately £199–£249 per month
Most private online prescribers charge a consultation fee (£15–£45) in addition to medication costs. Prices vary by provider — shopping around is worthwhile. Some private providers offer bundled packages including regular clinical reviews, which may provide better value long-term. Always check whether your chosen provider is GPhC-registered.
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 Mounjaro Access — What to Expect
NHS route: NICE has approved tirzepatide (Mounjaro) for weight management, but availability is through tier 3 specialist weight management services only — not standard GP prescription. You need referral from your GP, and waiting times vary dramatically by region (3–18 months in many areas). Once approved, Mounjaro is free on the NHS.
Private route: Faster access (prescription issued within 24–48 hours in many cases) without waiting lists. You'll complete an online clinical assessment with a UK-licensed prescriber, and if approved, the Mounjaro KwikPen is dispensed by a GPhC-registered pharmacy. This is the quicker option if you want to start a weekly weight loss injection sooner, but costs are your responsibility. Compare this against Wegovy — another GLP-1 option available privately — to find what suits your needs and budget.
- 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 quickly does Mounjaro start suppressing appetite after the first injection?
Many people report reduced appetite within 3–7 days of the first 2.5 mg injection, though this is the starting dose and effects intensify as you titrate upward. Full appetite suppression typically develops over weeks 4–12 as you progress through the dose escalation schedule. Individual responses vary — some feel it immediately, others notice gradual changes over several weeks.
What's the difference between NHS and private Mounjaro access timelines?
NHS access requires GP referral to specialist services, with waiting times of 3–18 months depending on your region. Private access is faster — most online prescriptions are issued within 24–48 hours following clinical assessment. If you cannot wait for NHS availability, private prescription is the quicker route, though you'll pay out of pocket.
Will I see weight loss results within the first month of Mounjaro?
Weight loss typically becomes visible during weeks 4–8, as you escalate from 2.5 mg to 5 mg and beyond. The first month (at 2.5 mg) focuses on tolerating the medication and allowing your body to adjust. Clinical trials showed meaningful weight loss developing after 8–12 weeks on the medication, alongside diet and activity changes.
Is Mounjaro cheaper on the NHS or through private prescription?
Mounjaro is free on the NHS if you're approved through specialist services, but waiting lists are long in many areas. Private prescription costs £129–£249 monthly depending on dose. If you need faster access, the private cost may be worth it; if you can wait, NHS access is free long-term. Budget 6–18 months for NHS referral.
How do Mounjaro costs compare to Wegovy for weight loss in the UK?
Both are prescription-only weekly weight loss injections available privately at similar price points (roughly £130–£250/month). Mounjaro (tirzepatide) is a dual GIP+GLP-1 agonist; Wegovy (semaglutide) is GLP-1 only. Clinical trial data suggests similar weight loss outcomes on average — choose based on prescriber recommendation, cost, and availability. Our free GLP-1 weight loss calculator can help you estimate expected outcomes alongside your chosen medication.
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.