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 2.5 mg for Weight Loss — What You Need to Know
Mounjaro 2.5 mg is the initial starting dose of tirzepatide, a prescription-only weekly weight loss injection licensed in the UK. This dose is not typically the dose where you remain — it's part of a gradual dose titration schedule designed to help your body adjust while minimising side effects. Understanding how the 2.5 mg starting dose works, what happens next, and whether this medication may be suitable for you requires insight into the full treatment pathway. Use our free GLP-1 weight loss calculator to explore potential outcomes at different doses, and consult your GP if you think prescription weight loss treatment might be appropriate for your circumstances.
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.
How Mounjaro 2.5 mg Works as a Starting Dose
Mounjaro 2.5 mg is not a treatment dose — it's a starting point for dose titration. You'll remain on 2.5 mg for weeks 1–4, during which your body adjusts to the medication's effects. The 2.5 mg dose activates both the GIP and GLP-1 hormone pathways, which may help reduce appetite and support feeling fuller after eating. At this low dose, side effects are typically minimal, though some people experience mild nausea or digestive changes. After 4 weeks, your prescriber will usually increase you to 5 mg, and the dose continues to escalate by 2.5 mg every 4 weeks until you reach a therapeutic dose (typically 10–15 mg). The stepped approach exists because jumping to a higher dose immediately can cause significant nausea and gastrointestinal side effects. A weekly weight loss injection like Mounjaro requires patience — the clinical benefits emerge over weeks and months as you progress through the dose schedule alongside dietary changes and increased physical activity.
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.
UK Prescription Access and Eligibility
In the UK, Mounjaro is available as a prescription-only medicine requiring clinical assessment before dispensing. Access varies: through NHS specialist weight management services (tier 3/4), where NICE has approved tirzepatide, or through GPhC-registered private prescribers following an online clinical consultation. NHS access typically requires referral from your GP and involves assessment by a specialist team — waiting times vary significantly by region. Eligibility generally includes adults with a BMI of 30 or above, or 25–29.9 with weight-related health conditions like type 2 diabetes or hypertension. For South Asian, Chinese, or Black African/Caribbean adults, eligibility may start at a lower BMI threshold. Your prescriber will assess your individual circumstances, medical history, and whether Mounjaro is suitable before issuing a prescription.
- 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.
Is 2.5 mg Mounjaro enough for weight loss?
No — 2.5 mg is the starter dose only. You'll progress to higher doses every 4 weeks (5 mg, 7.5 mg, 10 mg, 12.5 mg, 15 mg) over several months. Meaningful weight loss typically occurs at doses of 10 mg and above, based on clinical trial data. Your prescriber will adjust your dose based on your response and tolerance.
How much weight will I lose on Mounjaro 2.5 mg?
Little to no significant weight loss occurs at 2.5 mg alone — it's a tolerance-building dose. The SURMOUNT-1 trial showed average weight loss of 15–21% at higher doses (5–15 mg) alongside diet and exercise. Individual results vary considerably. Our GLP-1 weight loss calculator can help estimate potential outcomes.
How long will I be on the 2.5 mg dose?
Typically 4 weeks. You'll take one 2.5 mg injection per week for weeks 1–4, then progress to 5 mg if tolerated well. The full dose titration from 2.5 mg to a therapeutic dose takes approximately 16–20 weeks depending on your prescriber's protocol.
What side effects occur at 2.5 mg?
At the starting dose, side effects are usually mild or absent. Some people experience mild nausea, constipation, or reduced appetite — these often improve as your body adjusts. More pronounced side effects (nausea, diarrhoea) typically emerge at higher doses. Always inform your prescriber of any concerns.
Can I get Mounjaro on the NHS at 2.5 mg?
Yes — Mounjaro is available through NHS tier 3 specialist weight management services in some regions. You'll need referral from your GP and assessment by a specialist team. Availability and waiting times vary significantly across UK regions. Your GP can advise on access in your area.
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.