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 During Your Period — Medication Options in the UK
Weight fluctuations during your menstrual cycle are completely normal, and many people wonder how hormonal changes affect their weight management goals. If you're considering prescription weight loss medication in the UK, it's important to understand how your cycle may interact with these treatments. This guide explains UK-licensed weight management options, eligibility criteria, and practical considerations for managing weight loss while navigating monthly hormonal changes.
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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.
UK-Licensed Weight Loss Medications for Women
Three prescription-only weight loss injections are currently licensed in the UK for weight management: Mounjaro (tirzepatide), Wegovy (semaglutide), and Saxenda (liraglutide). These medications work by mimicking natural hormones that regulate appetite and blood sugar.
Mounjaro is a dual GIP and GLP-1 receptor agonist, helping users lose an average of 15–21% of body weight in clinical trials. Wegovy is a GLP-1 agonist with average weight loss of around 15% at the maximum dose. Both are injected once weekly. Saxenda, a daily injection, offers similar mechanisms and is also available through NHS and private channels.
Women are eligible if they have a BMI of 30 or above, or 27–29.9 with weight-related health conditions such as type 2 diabetes, high blood pressure, or cardiovascular disease. Eligibility is assessed individually by a prescriber following a clinical assessment. Use our free BMI calculator to check where you stand on the NHS scale and explore whether medication might be appropriate for your situation.
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 Access and Your Menstrual Cycle
NHS access is available through specialist tier 3 weight management services, typically requiring a GP referral. However, NHS waiting lists can be lengthy in many regions. Private access is available through GPhC-registered online pharmacies following an online consultation with a UK-licensed prescriber, without needing an NHS referral.
Regarding your period: hormonal fluctuations may affect appetite, water retention, and how you perceive weight changes. Some women find nausea (a common side effect of GLP-1 medications) is more pronounced during certain phases of their cycle. This is an important conversation to have with your prescriber during your clinical assessment. They can monitor your response and adjust your dose timing or support if needed. Track your weight loss progress using our free progress tracker to identify any patterns related to your cycle.
Starting any weight loss medication during your period is safe, though some women prefer to begin during the follicular phase (after menstruation ends) to distinguish medication side effects from hormonal symptoms. There is no medical reason to delay treatment based on cycle timing alone. However, if you take oral contraceptives, inform your prescriber—GLP-1 medications may reduce absorption of oral contraceptive pills, so a backup contraception method is recommended for 4 weeks after starting and after each dose increase.
- 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 I take Mounjaro or Wegovy during my period?
Yes, prescription weight loss injections are safe to take during menstruation. Some women find it helpful to start during the follicular phase (after their period ends) to better distinguish medication side effects from hormonal symptoms, but this is a personal choice. Discuss timing with your prescriber.
Will my period affect how well the medication works?
Hormonal fluctuations may influence appetite, water retention, and side effect perception, but will not reduce medication effectiveness. Your cycle may affect how you feel or perceive weight changes week to week. Tracking your progress over full menstrual cycles rather than weekly helps show true progress.
I'm on the contraceptive pill—can I take weight loss injections?
Yes, but your prescriber must know. GLP-1 medications may reduce oral contraceptive absorption, so you'll need to use a backup contraception method (like condoms) for 4 weeks after starting and after each dose increase. This is important for contraceptive reliability.
How do I know if I'm eligible for weight loss medication on the NHS?
You're eligible if you have a BMI of 30 or above, or 27–29.9 with weight-related health conditions. Use our free BMI calculator to check your status. For NHS access, speak to your GP about referral to specialist tier 3 weight management services in your area.
What's the difference between Mounjaro and Wegovy?
Mounjaro (tirzepatide) is a dual GIP+GLP-1 agonist with average weight loss of 15–21%. Wegovy (semaglutide) is a GLP-1 agonist with average weight loss around 15%. Both are once-weekly injections. Individual results vary significantly. Your prescriber will determine which is most suitable based on your health profile.
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.