At Prema Health in Portsmouth, one of the most common questions we hear from patients starting Mounjaro (tirzepatide) for weight loss is:
“Can it affect my periods?”
The short answer is yes — sometimes it can, though usually as a temporary side effect of your body adjusting to weight loss and hormonal changes, rather than a direct result of the medication itself.
How Mounjaro Works
Mounjaro helps with weight loss by mimicking natural hormones (GIP and GLP-1) that regulate blood sugar and appetite. It slows digestion, reduces hunger, and improves how the body uses insulin.
These changes often lead to significant and steady weight loss — but because hormones, metabolism, and reproductive health are closely linked, shifts in body composition can temporarily affect your menstrual cycle.
Why Period Changes Can Happen
There are a few reasons why Mounjaro may influence your cycle:
- Changes in body fat and oestrogen – Fat cells store oestrogen. As you lose fat, your oestrogen levels can fluctuate, which may cause your periods to become lighter, heavier, or irregular for a while.
- Metabolic adjustments – Rapid changes in diet and energy balance can temporarily disrupt how your brain and ovaries communicate, delaying ovulation or causing missed cycles.
- Improved hormone balance – For some people with conditions like PCOS, Mounjaro can actually regulate the menstrual cycle by improving insulin sensitivity and lowering androgen levels.
- Digestive changes and contraception – Because Mounjaro slows digestion, it can sometimes affect how oral contraceptives are absorbed, leading to spotting or breakthrough bleeding.
What You Might Notice
Some common cycle changes reported by Mounjaro users include:
- Irregular or skipped periods in the first few months
- Heavier or lighter bleeding
- Spotting between periods
- Altered PMS symptoms — sometimes milder than before
- Temporary absence of periods (amenorrhea) during rapid weight loss
Most people find their cycle settles down after a few months, once their weight stabilises and their body adapts to the medication.
When to Book an Appointment
Minor changes are usually nothing to worry about. However, we recommend booking a telephone appointment with one of our Prema Health Private GPs if you experience any of the following:
- Very heavy bleeding (for example, soaking through protection every hour)
- Bleeding that lasts longer than 7–10 days
- Severe pelvic pain
- No period for more than three months
- Bleeding after menopause
Our Private GPs can review your symptoms, check your iron levels, assess hormone balance, and ensure that your treatment plan remains safe and effective.
Supporting Your Cycle While on Mounjaro
A few simple steps can help keep your cycle steady while using Mounjaro:
- Track your periods – Use an app or diary to record timing, flow, and symptoms.
- Eat well – Make sure you’re getting enough nutrients and energy to support hormone balance.
- Be patient – Most irregularities improve within a few months.
- Discuss contraception – If you’re on the pill, consider a backup method while your body adjusts.
The Prema Health Perspective
Mounjaro may cause temporary menstrual changes as your body adapts to improved metabolism and reduced body fat. For many women, this is short-lived — and for some, especially those with previously irregular cycles, it can actually bring better cycle regularity over time.
If you’re using Mounjaro and notice changes to your periods, our team at Prema Health Portsmouth is here to help. Book a quick telephone consultation with one of our Private GPs, and we’ll guide you through what’s normal, what to expect, and how to keep your treatment — and your wellbeing — on track.