People have self-reported changes in their menstrual cycles after receiving COVID-19 vaccines, but research has not confirmed a link between these two.

Individuals reported that some of these differences include heavier bleeding and changes in menstrual cycle length.

Variations in a person’s menstrual cycle can happen for a variety of reasons. For example, a significant life event or major stressor may cause irregular periods. It is sometimes challenging for doctors to determine the exact cause of a change in the menstrual cycle.

Keep reading to learn more about the effect of COVID-19 vaccines on menstrual cycles.

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Health experts do not officially list changes in the menstrual cycle as known side effects of COVID-19 vaccines. That said, media reports about these changes following vaccination have encouraged researchers to study this effect.

However, the clinical studies on COVID-19 vaccines did not collect data on menstrual cycles, so researchers are unsure about the link. The Center for Disease Control and Prevention (CDC) Vaccine Safety Datalink also does not collect data on changes to the menstrual cycle.

If the vaccines have an effect, doctors are not sure why.

The Norwegian Institute of Public Health reports that COVID-19 vaccines may cause general bleeding disturbances or hormonal changes. These factors may explain changes in menstruation after receiving a COVID-19 vaccine. Nevertheless, researchers have not confirmed this theory.

Therefore, a significant lack of research means that the link between menstrual cycles and COVID-19 vaccines is unclear. Most of the evidence is anecdotal, but that does not mean the link does not exist — it just means researchers have not fully investigated it yet.

A 2022 study assessed if the COVID-19 vaccine changes menstrual cycles. Researchers compared changes in menstruation between vaccinated and unvaccinated people.

The results of the study showed a less than 1-day change in menstrual cycle length for both COVID-19 vaccine doses. People who were unvaccinated did not have significant changes in their menstrual cycle.

Therefore, the researchers concluded that COVID-19 vaccination may affect menstrual cycle length but not the duration of bleeding.

Another 2022 study distributed questionnaires to people who menstruate and were between the ages of 18–30 years. The participants had all received two COVID-19 vaccines.

They reported that while variations in menstrual cycle length occurred, they may be independent of vaccination.

Before vaccination, the researchers noted frequent menstrual disturbances among participants in the study. Variations in the menstrual cycle are common, and it is difficult to determine the exact cause. Stress, minor illnesses, and changes in medication can alter a person’s cycle.

However, people in this study reported that they had heavier menstrual bleeding after vaccination. Other reported changes included a longer bleeding period and shorter intervals between cycles.

It is unclear if the cause of these variations was vaccination. Doctors consider menstrual cycle length variation typical if it is under 8 days, but what is “normal” can vary from person to person.

Despite this, it is important to note that most menstrual changes following a COVID-19 vaccine were mild and temporary. Additionally, increases in menstrual cycle length were typically limited to 6 months following vaccination. These side effects were also more common in people who already had long, short, or irregular cycles. There is also no evidence to suggest that the vaccine affects fertility.

Read more about COVID-19 vaccinations and menstrual bleeding.

Participants in a 2022 study noticed a change in their menstrual cycles 1–14 days after receiving the COVID-19 vaccine. They reported heavier or lighter than usual bleeding.

Social media platforms, such as Twitter and Reddit, allow users to share their experiences and thoughts about vaccines, and many have taken to these spaces to discuss side effects. Anger and frustration over the lack of information about how the vaccine affects a person’s menstrual cycle are common.

While some people reported heavier and longer menstrual cycles, others noticed a delayed or skipped period. Individuals have also reported that their menstrual cycles have not changed since receiving both doses.

With changes in menstruation, some feel concerned that the vaccine has affected their fertility.

Some individuals have also discussed the changes they have experienced in their menstrual cycle after COVID-19 vaccination with their doctors. However, through these discussions with their doctors, some people have felt that their concerns were brushed off or ignored.

These effects on menstrual cycles can affect a person’s willingness to receive a second or subsequent dose. To prevent the spread of misinformation about COVID-19 vaccination and its effect on menstrual cycles, researchers and doctors must investigate this possible link.

Menstrual changes can occur for many different reasons. However, doctors may not always find the exact cause. Individuals with concerns about changes in their menstrual cycles after receiving a COVID-19 vaccination can speak with their doctor.

Research has not yet conclusively determined if an association exists between COVID-19 vaccination and menstrual cycle changes. However, the literature does show that vaccination may have led to a short-term trend toward longer cycles. That said, this should be no cause for concern, with no long-term implications.

If COVID-19 vaccines affect menstrual periods, the changes researchers reported in clinical studies were mild and short term. However, people should speak with a doctor about any heavy or prolonged menstrual bleeding.

Additionally, vaccination hesitancy may arise from reports about people experiencing a change in menstruation after receiving a dose. A person can speak with a doctor to learn about the benefits and risks of COVID-19 vaccination.

Doctors are uncertain whether COVID-19 vaccines cause changes in menstrual cycles. Research on menstrual cycle changes after COVID-19 vaccination shows temporary variations in bleeding and cycle length.

However, these changes are not likely dangerous.

Clinical studies on the effect of COVID-19 vaccines on menstrual cycles are inconclusive. Researchers need to continue their study to confirm whether a link exists between COVID-19 vaccines and changes in menstruation.