Heavy menstrual bleeding is most often caused by hormonal imbalances, structural growths in the uterus, or underlying bleeding disorders. A typical period involves losing about 2 to 3 tablespoons of blood over several days. When that amount exceeds 5 tablespoons, or your period stretches beyond seven days, it crosses into what doctors consider abnormally heavy bleeding.
The causes range from common and easily treated to serious conditions that need prompt attention. Understanding where heavy bleeding comes from helps you recognize what might be happening in your body and what kind of evaluation to expect.
How to Tell If Your Bleeding Is Actually Heavy
Since most people aren’t measuring their blood loss in tablespoons, the CDC offers more practical benchmarks. Your bleeding is likely heavier than normal if you need to change a pad or tampon after less than two hours, or if you’re soaking through one or more every hour for several hours straight. Needing to double up on pads, waking up at night to change protection, or passing blood clots the size of a quarter or larger are all signs that something beyond a normal period is going on.
Periods lasting more than seven days also qualify, even if the flow doesn’t seem extreme on any single day. The cumulative blood loss still adds up and can lead to iron deficiency over time, leaving you fatigued, short of breath, and low on energy.
Hormonal Imbalances
Your menstrual cycle depends on a carefully timed rise and fall of estrogen and progesterone. When these hormones fall out of sync, the uterine lining can build up more than usual before shedding, which produces a heavier, longer period. This is one of the most common causes of heavy bleeding across all age groups.
In teenagers, hormonal imbalance is especially common because the system controlling ovulation is still maturing. The brain and ovaries haven’t yet settled into a predictable rhythm, so cycles can be irregular and heavy for the first few years after periods begin. In women approaching menopause (typically in the 40s), hormone levels fluctuate unpredictably as the ovaries wind down. Estrogen may spike without enough progesterone to balance it, causing the uterine lining to thicken excessively before it sheds. Thyroid disorders can also throw off the hormonal balance that regulates periods, which is why thyroid function is one of the first things checked during an evaluation for heavy bleeding.
Fibroids and Polyps
Uterine fibroids are noncancerous muscle growths in the wall of the uterus. They’re extremely common, particularly in women over 30, and their size ranges from a seed to a grapefruit. Not all fibroids cause symptoms, but those that grow near the inner lining of the uterus can distort the cavity, increase its surface area, and interfere with the uterus’s ability to contract and stop bleeding after the lining sheds. The result is prolonged, heavy periods, often with large clots.
Uterine polyps are a different type of growth. These form when cells in the uterine lining overgrow, creating soft tissue that attaches to the inner wall by a base or thin stalk. Polyps cause irregular bleeding, very heavy flow, and spotting between periods. They’re generally small and benign, but they can occasionally harbor precancerous changes, so doctors typically recommend removing them for examination.
Adenomyosis
Adenomyosis happens when tissue from the uterine lining grows into the muscular wall of the uterus. Each month, that embedded tissue responds to hormones just like the normal lining does: it thickens, breaks down, and bleeds. But because it’s trapped inside the muscle, it causes the uterus to enlarge, become tender, and produce significantly heavier periods with clots. Bleeding between periods is also common.
The condition tends to develop after the uterine surface has been disrupted, such as during childbirth, pregnancy, or prior surgery. It’s most frequently diagnosed in women in their 30s and 40s. In the past, it was only confirmed after a hysterectomy, but advances in ultrasound and MRI now allow doctors to identify the characteristic uterine thickening without surgery.
Bleeding Disorders
Some women bleed heavily because their blood doesn’t clot properly. This is an underrecognized cause, especially in teenagers. The three most common bleeding disorders linked to heavy periods are von Willebrand disease (a genetic condition where a key clotting protein is defective or missing), platelet function disorders (where the cells responsible for clotting don’t work correctly), and carrier status for hemophilia, which can cause prolonged bleeding after injuries, easy bruising, and heavy menstrual flow.
Research from UT Southwestern Medical Center highlights that these disorders are among the top three causes of heavy periods in young women. Studies examining women with heavy menstrual bleeding have found von Willebrand disease in roughly 5 to 13 percent of cases, with platelet disorders sometimes even more common. Heavy periods are frequently the first and most noticeable symptom of an undiagnosed bleeding disorder, which is why blood-clotting tests are a standard part of the workup.
Medications That Increase Flow
Certain medications can make periods noticeably heavier. Blood thinners, including aspirin and prescription anticoagulants, reduce the blood’s ability to clot, which directly increases menstrual flow. This is a well-documented side effect and something to bring up with your prescribing doctor if your periods change after starting one of these medications.
Perhaps more surprising, common over-the-counter painkillers like ibuprofen and naproxen can also alter menstrual bleeding. While low doses of these drugs are sometimes used to reduce period flow, they belong to a class of anti-inflammatory medications that can affect how the uterine lining sheds and how blood clots form at the site.
Endometrial Cancer and Precancer
Heavy or unusual bleeding is the most prominent warning sign of endometrial cancer. About 90 percent of women diagnosed with endometrial cancer reported abnormal bleeding before their diagnosis, according to the National Cancer Institute. This is especially significant after menopause: roughly 9 percent of postmenopausal women who saw a doctor for unexpected bleeding were later diagnosed with endometrial cancer.
Rising obesity rates are thought to be a major driver of increasing endometrial cancer cases, because excess body fat produces extra estrogen, which stimulates the uterine lining to grow. Hormone replacement therapy can also cause bleeding, particularly in the first six months of use, which isn’t necessarily alarming. Persistent bleeding beyond that initial window, however, warrants testing. For premenopausal women, endometrial cancer is far less common, but persistently heavy or irregular bleeding that doesn’t respond to treatment still calls for further investigation.
How Doctors Find the Cause
An evaluation for heavy bleeding typically starts with a detailed history of your cycles, sometimes including a diary tracking days of bleeding and flow intensity. From there, doctors move through a series of tests depending on your age, symptoms, and risk factors.
Blood tests come first, checking for iron deficiency anemia, thyroid problems, and clotting abnormalities. An ultrasound uses sound waves to create images of your uterus and ovaries, revealing fibroids, polyps, or signs of adenomyosis. A Pap test screens for cervical changes. If those initial results suggest something in the uterine lining, an endometrial biopsy takes a small tissue sample to check for precancerous or cancerous cells.
When more detail is needed, a sonohysterography fills the uterus with fluid during an ultrasound to get a clearer view of the lining. A hysteroscopy inserts a thin, lighted scope through the cervix so the doctor can visually examine the inside of the uterus. These aren’t always necessary, but they help pinpoint growths or abnormalities that standard imaging might miss.
Why It Matters Beyond the Inconvenience
Chronic heavy bleeding does more than disrupt your daily life. The steady loss of blood depletes your iron stores over time, leading to anemia. Symptoms of anemia from heavy periods include persistent fatigue, shortness of breath, dizziness, and low energy that doesn’t improve with rest. Many women adapt to these symptoms gradually and don’t realize how much their quality of life has declined until the bleeding is treated and their iron levels recover.
Heavy bleeding also sometimes signals conditions that progress without treatment. Polyps can occasionally develop precancerous changes. Fibroids may continue to grow. Endometrial hyperplasia, where the lining thickens from excess estrogen without enough progesterone, can evolve into cancer if left unaddressed. Identifying and treating the underlying cause resolves the bleeding and prevents these longer-term complications.