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
Weight Loss and Menstruation: What You Need to Know
Weight loss can affect your menstrual cycle, and understanding this connection is important if you're considering weight management in the UK. gradual weight management, extreme calorie restriction, and significant body composition changes may temporarily disrupt or stop your period — a condition called amenorrhoea. If you're exploring prescription weight loss medication as part of your weight management journey, it's helpful to know how these treatments work alongside your reproductive health. This guide covers the relationship between weight loss and menstruation, and explains the prescription weight loss options available to eligible UK adults.
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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 in the UK
If you're looking to manage your weight safely in the UK, several prescription-only weight loss medications are now available through NHS specialist services and private prescribers. These are licensed for adults with a BMI of 30 or above, or 27 or above with weight-related health conditions such as type 2 diabetes, high blood pressure, or sleep apnoea.
The most commonly prescribed options are:
- Mounjaro (tirzepatide) — a once-weekly dual GIP/GLP-1 receptor agonist injection. Clinical trials showed participants lost an average of 15–21% of their body weight, though individual results vary.
- Wegovy (semaglutide) — a once-weekly GLP-1 receptor agonist injection. Evidence suggests an average weight loss of around 15% of body weight when combined with a reduced-calorie diet and increased physical activity.
- Saxenda (liraglutide) — a daily GLP-1 injection, approved for weight management in UK adults.
These medications work by helping to regulate appetite and supporting feeling fuller after meals. They're designed to be used alongside lifestyle changes — diet and exercise remain essential. Try our free GLP-1 weight loss calculator to explore potential outcomes at different doses, and use our BMI calculator to check whether you may meet eligibility criteria.
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.
How to Access Weight Loss Medication in the UK
Access to prescription weight loss medication in the UK depends on your route:
- NHS route: Your GP can refer you to a specialist tier 3 or 4 weight management service. Availability varies significantly by region, and waiting lists can be lengthy in many areas. Once referred, a specialist will assess your eligibility and prescribe if appropriate.
- Private route: You can access medication through a GPhC-registered online pharmacy following a consultation with a UK-licensed prescriber. This bypasses NHS waiting lists but involves costs typically ranging from £129–£320 per month depending on dose.
A prescriber will assess your individual health, including any menstrual or hormonal factors, before prescribing. If you experience significant changes to your menstrual cycle during weight loss treatment, discuss this with your GP or prescriber — they can advise on whether adjustments are needed.
- 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.
Can weight loss medication affect my period?
GLP-1 and GIP/GLP-1 medications don't directly target hormonal systems, but gradual weight management from any cause — including medication — can temporarily affect your menstrual cycle. Some people experience irregular periods or temporary amenorrhoea during significant weight loss. This typically resolves once weight stabilises. Always discuss menstrual changes with your GP or prescriber.
What is the safest rate of weight loss for my period to remain regular?
The NHS recommends losing 0.5–1 kg (1–2 lbs) per week for sustainable results. Slower, gradual weight loss is less likely to disrupt your menstrual cycle than rapid loss. Extreme calorie restriction (under 800 kcal/day) significantly increases the risk of amenorrhoea and should only be undertaken under medical supervision.
Am I eligible for prescription weight loss medication if I'm trying to conceive?
Mounjaro and Wegovy are not recommended during pregnancy or if you're trying to become pregnant immediately. However, reaching a healthy BMI before conception can improve fertility outcomes. Discuss your plans with your GP or a fertility specialist — they can advise on the best timing for weight management and medication use.
How does my BMI affect my menstrual health?
Both underweight (BMI under 18.5) and overweight/obese (BMI over 25) can affect menstrual regularity. Use our free BMI calculator to check where you fall, and aim for the healthy range of 18.5–24.9 (or 18.5–22.9 if you're of South Asian, Chinese, or Black African heritage). Your GP can advise on a safe target weight for your individual health.
Where can I find more information about weight loss medication in the UK?
Your GP is the best starting point — they can discuss your eligibility, explain the NHS pathway, and answer questions about how medication might affect your menstrual health. For general information, the NHS website and NICE guidance cover weight management options. Our GLP-1 weight loss calculator and progress tracker can also help you explore and monitor your weight management journey.
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.