Will the covid vaccine cause period changes and menstrual problems?

Will the Covid-19 Vaccines Cause Period Changes And Affect My Menstrual Cycle?

Doctor Khalid

Table of Contents

Summary of the latest data and science on whether covid vaccines change women's periods.

I have had a few patients ask me this exact question recently and as a family doctor working in the UK, I thought I'd take a deep dive and find out the latest research and data. Around 30,000 women had reported period changes to the MHRA in the UK via their yellow card system - a system set up to pick up any issues people might have after taking a medication/vaccine. Because period changes can affect up to 30% of women, the tricky part is working out whether it was down to the vaccine or a natural occurrence.

The Royal College of Obstetrics and Gynaecology (RCOG) recently released a statement on this that may help shed some light. The main take-home was that although nothing has been conclusively been linked to the vaccine, there is some biological plausibility and theories which could explain why so many women have been experiencing these. The two most important take-homes are:

1) If any changes do occur - seems to be only temporary and for a cycle or two.

2) The vaccine does not affect your fertility or future chances of having children.

Dr Jo Mountfield's (VP of RCOG) Thoughts on this: 
"There is no evidence to suggest that these temporary changes will have any impact on a person’s future fertility, or their ability to have children. It is important to get vaccinated as the best protection against coronavirus. This is especially important if you are planning a pregnancy, as we know unvaccinated pregnant women are more at risk of becoming seriously ill from COVID-19.
We support calls for more research to understand why women may be experiencing changes to their menstrual cycle after having the vaccine.”

The MHRA have themselves looked into the data surrounding the reports and have thus far concluded that there isn't a definitive link. They've said that based on the comparison between the usual prevalence of a common problem like period changes and the numbers reported there isn't actually enough evidence to support a link.

Biological Plausibility

Our brain, ovaries and womb interact to control the menstrual cycle. They work in unison as part of a hormonal system that is kept in equilibrium. Some scientists hypothesise that menstrual disturbance may be due to effects on the part of the brain that controls the reproductive hormones, effects on the ovaries or effects directly on the endometrium (lining of the womb which is what is shed during a period).

Physiologically we know that at times of stress, the female system is designed to temporarily downregulate to prevent pregnancy and help our bodies conserve energy. The idea is that at times like this the body will try and preserve as much energy for recovery and to protect itself.

The COVID-19 vaccination aims to initiate an immune response in the body to protect against future COVID-19 infection. Giving your body almost like a "trial run" of fighting something off similar to the virus itself. Our immune reaction to this could temporarily affect the ovaries, altering their hormone production over one or two cycles, resulting in irregular or heavier menstrual bleeding. The inflammation may also temporarily affect how the endometrium (womb lining) breaks down and sheds, causing a heavier period. It could be these possible effects that could explain why women have reported changes to their periods.

Because that initial immune response is only temporary it is important to remember that any effects of the vaccine are likely to be short-lived and much less severe than those associated with a Covid infection.


I think more robust data is needed for us to be sure of the initial findings. It is clear though that any changes that may occur can cause stress and anxiety in patients after vaccination, which is why it is so important to take these reports so seriously. Imagine if you didn't know that one of the side effects of the vaccine was a temperature or a sore arm - as soon as you got home - you would be frightened if you got any of these symptoms.

I also feel that if we don't research and draw more decisive conclusions then there are people who can take advantage of peoples anxieties and push misinformation and conspiracy theories. After all, if people have period changes that they may not have expected, it wouldn't be a stretch for them to suddenly fall for fertility misinformation. In next weeks blog post, I'll look at the science and evidence around the Covid-19 vaccine and fertility.

Ps I hope this has been useful, if you have found it of some value - feel free to share it with any friends or colleagues who may be worried about the same issues.

Have a wonderful day,

Doctor Khalid