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
How Weight Loss Affects Your Menstrual Cycle
Weight loss can affect your menstrual cycle in various ways, from timing changes to temporary disruptions. Understanding this connection helps you manage your health effectively during your weight management journey. Whether you're losing weight through diet, exercise, or prescription weight loss medication, hormonal shifts are a normal part of the process. This guide explains what happens, when to seek medical advice, and how to support your reproductive health while working towards a healthier weight.
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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.
The Hormone Connection: How Weight Loss Affects Your Period
Weight loss triggers hormonal changes that directly impact your menstrual cycle. Oestrogen is stored in body fat, so when you lose weight, oestrogen levels drop. This can affect the hormonal signals that regulate your period, potentially causing irregular cycles, lighter or heavier periods, or temporary amenorrhea (missing periods).
The speed of weight loss matters significantly. gradual weight management (more than 1.5 kg per week) is more likely to disrupt your cycle than gradual, sustainable weight loss. The NHS recommends losing 0.5–1 kg per week for this reason. If you're using prescription weight loss medication as part of your weight management plan, your GP can assess whether your rate of loss is appropriate for your individual health.
- Very gradual weight management can suppress the hormones needed to regulate menstruation
- Gradual weight loss typically causes fewer or milder disruptions
- Menstrual changes are usually temporary and resolve as your body adapts
- Nutritional deficits during weight loss can also contribute to cycle irregularities
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.
When to Expect Menstrual Changes and What's Normal
Menstrual changes during weight loss are common and usually temporary. You might experience lighter periods, longer gaps between periods, or occasional missed periods as your body adjusts. Most women's cycles stabilise within 3–6 months once weight loss slows or plateaus.
However, if you're experiencing prolonged amenorrhea (missing periods for more than 3 months), very heavy bleeding, or severe pain, contact your GP. These may indicate nutritional deficiencies, excessive weight loss, or other underlying health issues. Your GP can check your hormone levels and overall health. Track your cycle using our free progress tracker to monitor patterns and share this information with your healthcare provider if concerns arise.
Weight loss and healthy weight management are supported by multiple approaches. Using our BMI calculator, you can track where your current weight sits within NHS guidelines and set realistic targets. For those considering prescription weight loss medication—such as GLP-1 injections—discuss any concerns about menstrual health with your prescriber during your clinical assessment. These medications work alongside lifestyle changes, so your GP or prescriber can monitor your overall health, including menstrual patterns, throughout your weight management journey.
- 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.
Will my period come back if I lose weight too quickly?
If gradual weight management has disrupted your cycle, your period typically returns once weight loss slows and you're eating enough nutrients. However, prolonged amenorrhea requires GP assessment. Aim for 0.5–1 kg weekly loss. Your GP can advise on safe weight loss rates for your health.
Can weight loss medication affect my menstrual cycle?
GLP-1 weight loss medications (like those used in prescription weight management) work by affecting appetite and digestion, not directly by disrupting hormones. However, the weight loss itself may cause cycle changes. Any menstrual concerns during medication use should be discussed with your prescriber.
Should I stop losing weight if my period becomes irregular?
Not necessarily—irregular periods during weight loss are common and usually temporary. However, if your period stops for more than 3 months, you lose excessive weight rapidly, or you experience severe symptoms, contact your GP. They can assess whether your weight loss approach is safe for you.
How does the menstrual cycle affect weight loss progress?
Your menstrual cycle can influence weight fluctuations and appetite due to oestrogen and progesterone changes. You may retain slightly more water before your period, making weekly weight loss less visible. Track your progress over monthly cycles rather than week-to-week for a clearer picture of actual fat loss.
Is it safe to use weight loss injections if I want to get pregnant?
Most prescription weight loss medications are not recommended during pregnancy planning or pregnancy. If you're considering pregnancy or taking weight loss medication, discuss this with your GP or prescriber. They can advise on timing and safe weight management before conception.
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.