Symptom · Pelvis & genitals

Heavy periods

Also known as: menorrhagia, heavy menstrual bleeding, HMB, flooding

Menstrual bleeding that is heavier or lasts longer than usual and gets in the way of daily life. A measured loss of more than about 80 mL a cycle is the textbook threshold, but blood loss is rarely measured; in practice heavy periods mean needing to change a pad or tampon every one to two hours, using two forms of protection at once, passing clots larger than about 2.5 cm, bleeding through clothes or bedding, or bleeding for more than seven days. The blood comes from the endometrium, the lining of the uterus that is shed each cycle, and loss is increased by anything that enlarges the cavity, thickens the lining or weakens clotting. The pattern matters: regular but heavy periods, irregular heavy bleeds after long gaps, and heavy periods with bleeding in between point to different causes. Persistent heavy loss is a leading cause of iron deficiency anaemia. The same assessment applies to trans men and non-binary people who have periods. Heavy periods are worth raising with a GP whenever they interfere with daily life, school or work, because they can be assessed and treated; they do not have to be put up with.

Seek urgent care if

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Common causes

No underlying cause foundIn a large proportion of cases examination and tests are normal; the periods are regular but heavy, and treatment is directed at the bleeding itself.
Fibroids and polypsBenign growths of the uterine muscle (fibroids) or of the lining (endometrial polyps) enlarge the bleeding surface; fibroids that bulge into the cavity cause the heaviest bleeding.
Adenomyosis and endometriosisEndometrial-like tissue within the muscle wall of the uterus (adenomyosis) typically causes heavy, painful periods with a bulky, tender uterus; endometriosis, where similar tissue grows outside the uterus, more often causes painful periods, pain during or after sex and pelvic pain, and can occur alongside it.
Irregular ovulationWhen ovulation is infrequent, as in polycystic ovary syndrome, the first years after periods start and the years before the menopause, oestrogen thickens the lining without the progesterone that would normally mature and stabilise it, so there is no orderly withdrawal bleed and the lining is shed late, heavily and unpredictably.
Copper intrauterine deviceThe non-hormonal coil often makes periods heavier and longer, particularly in the first few months after it is fitted.

Less common causes

Bleeding disorders and anticoagulant medicinesInherited clotting problems such as von Willebrand disease (heavy periods since the very first period, easy bruising, nosebleeds) and anticoagulant medicines increase menstrual loss.
Thyroid diseaseAn underactive thyroid can make periods heavier and more frequent, which is why thyroid function is checked when other features suggest it.
Endometrial hyperplasia and cancerOvergrowth or cancer of the uterine lining is more likely over 45, with obesity, polycystic ovary syndrome or long gaps between periods, and when heavy periods come with bleeding between periods or after sex; it is investigated with ultrasound of the lining and an endometrial biopsy.
Pelvic inflammatory diseaseInfection of the uterus and tubes can cause heavy or irregular bleeding with pelvic pain, unusual discharge and fever.
Early pregnancy lossA miscarriage can be mistaken for a late, heavy period with clots, so a pregnancy test is part of the assessment of any unusually heavy bleed.

Often occurs with

Pelvic painUnusual vaginal bleedingFatigueDizziness

Conditions to read about

FibroidsEndometriosisPolycystic ovary syndromeAnaemiaUnderactive thyroid (hypothyroidism)

How it is investigated

Full blood countFerritin testThyroid function testsPregnancy testHormone testsBiopsy
UltrasoundMRI scan
Educational content. This page explains what a symptom can mean so that the anatomy and the medical reasoning make sense. It cannot tell you what is causing yours: only a clinician who can examine you and order tests can do that.