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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Tirzepatide 5 Mg: Dose, Effects, and UK Information
Tirzepatide 5 mg is the first maintenance dose of Mounjaro, a prescription-only weight loss injection licensed in the UK. At this dose, tirzepatide works as a dual GIP and GLP-1 receptor agonist to support appetite regulation and weight management. Clinical trials showed that adults on the 5 mg dose lost an average of approximately 15% of their body weight over 72 weeks, though individual results vary significantly. This dose typically comes after a 4-week starting phase at 2.5 mg. Use our free GLP-1 weight loss calculator to explore potential outcomes at different doses.
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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 Tirzepatide 5 Mg Works and What to Expect
Tirzepatide is a dual GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 receptor agonist — this dual mechanism sets it apart from single-mechanism weight loss injections. At the 5 mg dose, it activates both hormone pathways to help reduce appetite, support feeling fuller after eating, and slow gastric emptying. In the SURMOUNT-1 clinical trial, participants on 5 mg tirzepatide experienced an average weight loss of around 15% body weight alongside a reduced-calorie diet and increased physical activity.
- GIP activation: Helps regulate fat utilisation and may enhance weight loss compared to GLP-1 alone
- GLP-1 activation: Reduces hunger signals and supports appetite control
- Gastric effects: Slows stomach emptying, which may reduce gradually over time
- Individual variation: Results depend on adherence, diet, exercise, and personal metabolism
The 5 mg dose is injected once weekly using a pre-filled KwikPen. Most people remain on this dose for 4 weeks minimum before escalating to 7.5 mg if clinically appropriate. Your prescriber will assess whether to increase based on your response and tolerance.
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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.
Eligibility, Side Effects, and NHS Access in the UK
In the UK, tirzepatide (Mounjaro) may be prescribed to adults with a BMI of 30 or above, or BMI of 27–29.9 with weight-related health conditions such as type 2 diabetes, high blood pressure, or cardiovascular disease. For South Asian, Chinese, Black African, or Black Caribbean adults, lower BMI thresholds may apply. Use our free BMI calculator to check your personal BMI and understand your starting point.
Common side effects at 5 mg include: nausea, diarrhoea, constipation, and stomach pain — most tend to improve over time. Serious side effects are rare but include severe abdominal pain (possible pancreatitis) and severe allergic reactions, which require urgent medical attention.
NHS access is through specialist tier 3/4 weight management services — referral from your GP is typically required. Private access is available through online prescribing following a clinical assessment. Regional NHS availability varies significantly.
- 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 tirzepatide 5 mg the starting dose?
No. The starting dose is 2.5 mg for weeks 1–4. Tirzepatide 5 mg is the first maintenance dose, typically used from weeks 5–8. Your prescriber will increase to this dose after you've tolerated the starting dose, provided there are no concerning side effects or contraindications.
How much weight can I expect to lose on tirzepatide 5 mg?
Clinical trials showed an average of approximately clinically studied weight loss at the 5 mg dose over 72 weeks alongside diet and exercise. However, individual results vary significantly depending on adherence, metabolism, starting weight, and lifestyle factors. Your actual results may differ from the average.
Is tirzepatide 5 mg available on the NHS in the UK?
Yes, tirzepatide is NICE-approved and available on the NHS through specialist weight management services. However, access varies by region and requires referral from your GP. Private access is also available through online prescribing following a clinical assessment by a UK-licensed prescriber.
What are the most common side effects of tirzepatide 5 mg?
The most common side effects are nausea, diarrhoea, constipation, and abdominal pain. These affect more than 1 in 10 people and typically improve over the first few weeks as your body adjusts. Nausea is the most frequently reported side effect but often resolves over time.
How long do I stay on tirzepatide 5 mg before increasing the dose?
You should remain on the 5 mg dose for a minimum of 4 weeks (weeks 5–8) before your prescriber considers increasing to 7.5 mg. This allows time to assess your tolerance and response. Your prescriber will decide whether escalation is appropriate based on your individual progress and how well you've tolerated the dose.
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.