Health Topic

Menstruation

Menstruation (or period) happens monthly. As the uterus sheds its lining, vaginal bleeding follows. Menstrual blood is made of blood and tissue.

Reviewed Reviewed by a registered pharmacistGeneral information

Also called: Menses · Menstrual period · Period

Important: This page is general information, not medical advice. It does not recommend or prescribe any treatment. Always consult your doctor or pharmacist before starting, stopping or changing any medicine.

About Menstruation

Menstruation, also called a period, is normal vaginal bleeding that happens as part of the monthly cycle in women and girls. Every month, the body prepares for pregnancy. If pregnancy does not happen, the uterus (womb) sheds its lining. This blood and tissue leave the body through the vagina.

The menstrual cycle is the monthly process the body goes through to prepare for pregnancy. It is counted from the first day of one period to the first day of the next. Most menstrual cycles last about 28 days, but cycles can be shorter or longer and still be normal.

Most girls start having a period between ages 9 and 15, but some may start earlier or later. A period usually lasts three to seven days and can be light or heavy. It may take a few years to become regular.

Your period may change during times that affect hormones, such as after childbirth or while breastfeeding. Periods usually continue until menopause, which most often happens between ages 45 and 55.

In addition to vaginal bleeding, you may have:

  • Cramping pain in the lower abdomen (belly) or pelvis
  • Lower back pain
  • Bloating
  • Sore breasts
  • Food cravings
  • Mood swings or irritability
  • Headaches or fatigue

Premenstrual syndrome (PMS) is a group of physical and emotional symptoms that can happen in the days before a period starts. Many women have some PMS symptoms, which usually go away after their period begins.

Many women and girls use menstrual products such as pads, tampons, menstrual cups, or period underwear to manage bleeding during their period. Changing or cleaning these products often helps you stay comfortable and clean.

Menstrual irregularities are changes in the usual menstrual cycle. These may include missed periods, irregular periods, or heavy bleeding. Common menstrual irregularities include:

  • Amenorrhea means not having a period.
  • Oligomenorrhea means having periods that happen less often.
  • Menorrhagia means very heavy menstrual bleeding.
  • Prolonged menstrual bleeding occurs when periods regularly last longer than 8 days.
  • Dysmenorrhea refers to painful periods that may include severe cramps.

Keep track of your period each month. This can help you understand your usual cycle, know when to expect your next period, and notice changes.

Talk with your health care provider if you notice major changes in your menstrual cycle, very heavy bleeding, or severe pain. These may be signs of other health problems that need treatment.

It sits within Women, Endocrine System and Female Reproductive System.

The lead U.S. institute for this subject is the Eunice Kennedy Shriver National Institute of Child Health and Human Development.

When to speak to someone. Reading about a topic cannot tell you whether it applies to you. Speak to a doctor or pharmacist if symptoms are severe, sudden, getting worse, or simply not going away — and seek emergency care immediately for chest pain, breathing difficulty, sudden weakness or confusion, or a serious allergic reaction.

Research on Menstruation

1,311 studies areregistered for this condition on ClinicalTrials.gov, the U.S. National Library of Medicine's public registry. A selection is below — the links go straight to the registry entry, not to a summary of ours.

What a registered study does and does not mean. Registration means a study exists and has been declared publicly. It says nothing about whether the treatment being tested works, is safe, or is available to you. Many studies find no benefit — that is what research is for. Never seek out an experimental treatment on the strength of a registry entry alone.

Research currently under way

Research already completed

Study data from ClinicalTrials.gov, a service of the U.S. National Library of Medicine. Retrieved 2026-07-30. Registry entries are supplied by study sponsors and investigators; ClinicalTrials.gov does not verify their scientific validity. PocketsInfo is not affiliated with, and not endorsed by, the NLM or the NIH.

Where to read more

Rather than paraphrase, we point you to the primary sources. Every link below is to a government health agency, a national institute or a recognised medical body — grouped by what you are trying to find out.

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Diagnosis and Tests

Treatments and Therapies

Related Issues

Clinical Trials

Medical subject headings

Clinicians and researchers index this subject under Menstruation, Menstruation Disturbances. These are the terms to use when searching medical literature.

This page is built from the MedlinePlus health topic record for Menstruation, a service of the U.S. National Library of Medicine (NLM), National Institutes of Health. Information is from MedlinePlus.gov. PocketsInfo is not affiliated with, and is not endorsed by, the NLM or the NIH. Retrieved 30 July 2026.