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COVID-19 Vaccines May Cause Minor, Temporary Changes In Menstrual Cycles

Experts say these mild disruptions should not discourage someone from getting a COVID-19 vaccine.

They also note that other factors, including stress, can cause disruptions to a menstrual cycle.

The COVID-19 vaccine could lead to mild, temporary changes in the length of your menstrual cycle, according to a study published today in the journal Science Advances.

Nonetheless, experts say vaccines remain one of the best ways to avoid serious illness from the novel coronavirus.

The study looked at responses by 35,000 premenopausal and postmenopausal individuals about their menstrual cycle in the weeks after receiving a COVID-19 vaccine.

None of the participants had been diagnosed with COVID-19. Researchers excluded those between 45 and 55 to avoid confusion with irregular periods due to premenopause or postmenopause.

Reports say:

  • 42% of menstruating individuals reported a heavier flow after receiving the vaccine. Some experienced this within the first 7 days. Others did so between 8 and 14 days after receiving the vaccine.

  • Nearly 44% reported no changes

  • 14% reported a mix of no change or a lighter flow


  • Respondents who had experienced a pregnancy were most likely to report heavier bleeding.

  • Most non-menstruating premenopausal respondents on hormonal treatments experienced breakthrough bleeding.

  • More than 70% of respondents using long-acting reversible contraception, such as an IUD, experienced breakthrough bleeding.

  • Slightly more than 38% of those undergoing gender-affirming hormone treatments reported breakthrough bleeding.

The scientists said they believe the menstrual changes are usually short-term.

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