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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Mirena Coil and Weight Loss in the UK
The Mirena coil is an effective contraceptive, but many women experience weight gain as a side effect due to the progestin it releases. If you've gained weight with the Mirena and want to lose it, prescription weight management options are available in the UK. These include GLP-1 receptor agonist medications like Mounjaro and Wegovy, which are licensed for weight loss in eligible adults. This guide explains your options, how to assess your eligibility, and how to have a conversation with your GP about weight management alongside your contraceptive choice.
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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.
Prescription Weight Loss Options Available in the UK
If you're managing weight gained from the Mirena coil, several prescription weight loss medications are available in the UK for eligible adults. These include:
- Mounjaro (tirzepatide) — A once-weekly injection that activates dual GLP-1 and GIP pathways. Clinical trials showed participants lost an average of 15–21% of their body weight alongside reduced-calorie diet and increased physical activity. Doses range from 2.5 mg to 15 mg weekly.
- Wegovy (semaglutide) — A once-weekly GLP-1 injection. In clinical trials, participants lost approximately 14.9% of body weight at the maximum dose. Doses range from 0.25 mg to 2.4 mg weekly.
- Saxenda (liraglutide) — A daily GLP-1 injection for weight management, though less commonly prescribed than Mounjaro and Wegovy.
All three are prescription-only medicines requiring clinical assessment before being prescribed. They work best alongside lifestyle changes including reduced-calorie diet and increased physical activity. Individual results vary significantly.
Clinically BackedWeight Loss
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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 and How to Access Weight Loss Treatment
To be eligible for prescription weight loss medication in the UK, you typically need a BMI of 30 kg/m² or above, or a BMI of 27–29.9 with weight-related health conditions such as type 2 diabetes, high blood pressure, or sleep apnoea. Start by using our free BMI calculator above to check your current BMI. If you're eligible, speak with your GP about prescription weight loss options. You can access treatment through the NHS via specialist tier 3 weight management services (though waiting times vary by region), or privately through GPhC-registered online prescribing services following a clinical assessment. Your GP can discuss whether these medications are suitable for you alongside your current contraceptive.
- 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.
Does the Mirena coil always cause weight gain?
No, but it's a common side effect. The Mirena releases a small amount of progestin into the body, which can increase appetite and reduce metabolic rate in some women. Weight gain averages 1–3 kg over five years, but individual experiences vary. Some women experience minimal weight change, whilst others gain more.
Can I use weight loss medication if I have a Mirena coil?
Yes, prescription weight loss medications like Mounjaro and Wegovy can be used alongside the Mirena coil. However, you should discuss this with your GP or prescriber to ensure there are no interactions and to manage your overall contraceptive and weight health together.
What is the fastest way to lose weight from Mirena?
There is no assured "fastest" way, but combining a modest calorie deficit (around 500 kcal per day), increased physical activity, and potentially prescription medication (if eligible) offers the best chance of sustainable weight loss. The NHS recommends losing 0.5–1 kg per week for long-term success.
How do I know if I'm eligible for prescription weight loss treatment?
Use our free BMI calculator on this page to check your BMI. If your BMI is 30 or above, or 27–29.9 with weight-related health conditions, you may be eligible. Speak with your GP for personalised assessment and to discuss options available to you in your area.
Will weight loss medication work if I keep the Mirena coil in?
Yes, prescription weight loss medication can still be effective with the Mirena in place. The medication works independently of contraceptive hormones. However, weight loss may be slower if the Mirena continues to influence your appetite. Discuss with your GP whether keeping or removing the coil fits your overall health goals.
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.