Do COVID vaccines cause heavier periods? Agency recommends listing it as side effect

It’s not uncommon to experience side effects after getting a COVID-19 vaccine, including feeling generally unwell.

But should some people expect the shots to result in heavier menstrual bleeding?

The European Medicines Agency’s safety committee on Oct. 28 recommended listing heavier periods as a side effect of mRNA COVID-19 vaccines made by Pfizer and Moderna, according to a news release. The EMA is in charge of evaluating medicinal products for the European Union.

Specifically, the committee is advising that temporary heavier menstrual bleeding “of unknown frequency” should be included on both Pfizer’s and Moderna’s vaccine product information, the EMA said. This comes after a review of available data and published medical studies.

A few studies examining the potential impacts of COVID-19 vaccines on periods have been published in 2022. One found thousands who received two vaccine doses experienced altered menstruation, including heavier periods or breakthrough bleeding, McClatchy News previously reported. The study, funded by the National Institutes of Health, was published July 15 in the journal Science Advances.

“Heavy menstrual bleeding (heavy periods) may be defined as bleeding characterised by an increased volume and/or duration which interferes with the person’s physical, social, emotional and material quality of life,” the EMA’s release said.

Those who have received their first, second or third (booster dose) of Pfizer’s and Moderna’s vaccines have reported heavier periods, according to the EMA.

As of Nov. 1, the Food and Drug Administration has not identified a safety signal, meaning a potential safety issue, “for changes in menstrual cycles or heavy menstrual bleeding following COVID-19 vaccines,” Abby Capobianco, the agency’s press officer, told McClatchy News in a statement.

“The agency will continue to monitor for potential side effects of the authorized and approved COVID-19 vaccines and will consider labeling changes as warranted,” Capobianco added.

Here’s what else to know about COVID-19 vaccines and periods.

Do COVID vaccines cause heavier periods?

The EMA said its safety committee “concluded that there is at least a reasonable possibility that the occurrence of heavy menstrual bleeding is causally associated with these vaccines.”

Since people began to receive the COVID-19 shots, anecdotal reports emerged online about changes in menstruation, including heavier periods, according to The Washington Post.

In the study published in Sciences Advances, of those with regular periods, 42% said they had heavier bleeding after at least one dose of a COVID-19 vaccine. The work involved researchers from the Washington University School of Medicine in St. Louis and the University of Illinois at Urbana-Champaign.

In comparison, about 44% of participants reported their flow did not change, and roughly 14% experienced a mix of a lighter flow or no change, according to the research.

The study surveyed 39,129 people ages of 18 to 80 who mostly received Pfizer’s or Moderna’s COVID-19 vaccines and reported they never tested positive for COVID-19. The survey was launched on April 7, 2021, and collected responses until June 29, 2021.

“Generally, changes to menstrual bleeding are not uncommon or dangerous, yet attention to these experiences is necessary to build trust in medicine,” study authors wrote.

Additionally, some people who formerly menstruated but not longer do reported breakthrough bleeding.

One of the study’s authors, Kathryn Clancy, of the University of Illinois at Urbana-Champaign’s department of anthropology, told Science that she experienced an unusually heavy period 10 days after getting her first COVID-19 vaccine dose in early 2021, characterizing it as “menstrual flooding.”

Another study, which is undergoing peer review and was submitted to BJOG: An International Journal of Obstetrics and Gynaecology, examined the effects of COVID-19 vaccines on menstrual bleeding in 9,555 participants.

The research found that a “larger proportion” of those vaccinated, specifically about 40 people out of 1,000 individuals, experienced heavier bleeding after their first COVID-19 vaccine dose. Ultimately, the study concluded that COVID-19 vaccination can increase the chances of heavier periods.

One woman, Olivia Rodriguez, 26, told The Washington Post that she had a “bad experience” with her period after getting a second dose of the Moderna COVID-19 vaccine in March 2021.

Before Rodriguez got her second dose, she finished her period, according to the outlet. However, within days of receiving the additional dose, she started her period again with heavier bleeding than before, she told The Washington Post. Because of this, she does not intend to get a booster.

More on COVID vaccines and periods

A study published Jan. 5 in Obstetrics and Gynecology, which received NIH funding, found that one dose of a COVID-19 vaccine is linked to “a small change in cycle length,” McClatchy News previously reported.

Menstruating people who got the shot had slightly longer cycles, with their period starting a little later than expected, according to the research. Overall, the slight change was just under a one-day increase in the menstrual cycle length, “a longer time between bleeding,” the NIH said in a news release, and it didn’t affect the actual length of a person’s period, according to the study.

In September, the NIH announced a large international study, published in the British Medical Journal, which confirmed the findings of the Jan. 5 study. The research involved 19,622 participants.

“Covid-19 vaccination is associated with a small and likely to be temporary change in menstrual cycle length,” the study concluded.

However, the research did not report a change in menstrual bleeding among its participants.

“Future work should assess other aspects of changes to menstrual cycles, such as unexpected vaginal bleeding, menstrual flow and pain, and define the mechanism by which the postvaccination menstrual changes described here occur,” study authors wrote.

Common side effects after getting a COVID-19 vaccine include feeling fatigued and having a headache, chills, fever and muscle pain, according to the Centers for Disease Control and Prevention.

McClatchy News also contacted the CDC for comment regarding the EMA safety committee’s recommendation.

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