Heavier periods can result from structural changes in the uterus, hormonal imbalances, underlying medical conditions, medications, or simply the stage of life you’re in. Clinically, a period is considered heavy when total blood loss exceeds 80 mL per cycle or bleeding lasts longer than 7 days. In practical terms, that looks like soaking through a pad or tampon every hour for several hours, passing clots the size of a quarter or larger, or needing to double up on pads to keep up with the flow.
Most people with heavy periods have one or more identifiable causes. Here’s what could be behind the change.
Hormonal Imbalance: Too Much Estrogen, Not Enough Progesterone
Your menstrual cycle depends on a balance between estrogen and progesterone. Estrogen builds up the uterine lining each month, and progesterone keeps that buildup in check. When your body produces too much estrogen relative to progesterone, the lining grows thicker than it should. A thicker lining means more tissue to shed, which means a heavier, longer period.
This imbalance, sometimes called unopposed estrogen, can happen for several reasons. Irregular ovulation is one of the most common. When you don’t ovulate in a given cycle, your body never produces the burst of progesterone that normally follows. Without that signal, estrogen keeps stimulating the lining unchecked. The lining eventually breaks down on its own, but unevenly and often with heavier or more prolonged bleeding than a normal period. Conditions like polycystic ovary syndrome (PCOS) frequently cause this pattern because ovulation is skipped or delayed. Excess body fat also contributes, since fat tissue produces its own estrogen.
Fibroids and Adenomyosis
Uterine fibroids are noncancerous growths in the wall of the uterus. They’re extremely common, and depending on their size and location, they can significantly increase menstrual bleeding. Fibroids that grow into the uterine cavity or distort its shape tend to cause the heaviest periods because they increase the surface area of the lining and can interfere with the uterus’s ability to contract and stop bleeding.
Adenomyosis is a related but distinct condition where tissue similar to the uterine lining grows into the muscular wall of the uterus. This causes the uterine wall to become thicker and stiffer than normal. That stiffness disrupts the chemical signaling that normally controls menstrual blood loss. In a healthy uterus, specific enzymes and hormonelike compounds regulate how blood vessels constrict and how tissue repairs itself after shedding. In adenomyosis, the increased tissue rigidity throws off these pathways, leading to heavier and often more painful periods. Adenomyosis is particularly common in women in their 30s and 40s and is frequently underdiagnosed.
Perimenopause and Life Stage Changes
If your periods suddenly become heavier in your late 30s or 40s, perimenopause is a likely explanation. During this transition, which can last several years before menopause, ovulation becomes unpredictable. Some cycles you ovulate normally, others you don’t ovulate at all. In cycles without ovulation, the corpus luteum (the structure that produces progesterone after an egg is released) never forms, so progesterone stays low. The uterine lining keeps thickening under estrogen’s influence, then eventually breaks down unevenly.
This is the mechanism behind what’s sometimes called “flooding,” a sudden, very heavy gush of bleeding that can soak through clothing. Flooding episodes are unsettling but common during perimenopause. They’re the result of weeks of lining buildup shedding all at once rather than gradually over several days.
Periods can also be heavier at the other end of the reproductive spectrum. Adolescents in their first year or two of menstruation often have anovulatory cycles as their hormonal systems mature, which can produce unpredictably heavy bleeding.
Thyroid Problems
An underactive thyroid (hypothyroidism) is a surprisingly common cause of heavier periods. Low thyroid hormone disrupts the chain of hormonal signals your brain sends to your ovaries, which can lead to skipped ovulation and the same kind of lining overgrowth described above. But hypothyroidism also has a more direct effect: it changes how your blood clots. With reduced clotting efficiency, bleeding from the shedding uterine lining takes longer to stop and the total volume increases.
Because thyroid problems develop gradually, many people don’t connect their heavier periods to other symptoms like fatigue, weight gain, or feeling cold. A simple blood test can identify hypothyroidism, and treating it often brings periods back to a more manageable flow.
Bleeding Disorders
Some people bleed heavily during their periods because their blood doesn’t clot properly. Von Willebrand disease is the most common inherited bleeding disorder, and it disproportionately affects people with uteruses. Among women with chronic heavy menstrual bleeding, somewhere between 5% and 24% turn out to have Von Willebrand disease when tested, according to the American College of Obstetricians and Gynecologists. That’s a significant number, yet the condition is often missed because heavy periods get attributed to other causes first.
Clues that a bleeding disorder might be involved include heavy periods starting from your very first cycle, frequent nosebleeds, easy bruising, prolonged bleeding after dental work or surgery, and a family history of bleeding problems. Platelet disorders and other clotting factor deficiencies can produce similar patterns.
The Copper IUD
If your periods got heavier after having an IUD placed, the device itself may be the cause. The copper IUD (sold as Paragard in the U.S.) is well known for increasing menstrual blood loss. In studies, average blood loss went from about 59 mL per cycle before insertion to about 91 mL afterward, an increase of roughly 55%. For most people, this stays within a tolerable range and doesn’t lead to iron deficiency. But if your baseline was already on the heavier side, that additional 55% can push you into territory that feels unmanageable.
Hormonal IUDs, by contrast, typically reduce menstrual bleeding over time. Blood thinners (anticoagulants) and certain anti-inflammatory medications can also increase flow.
Polyps and Other Growths
Endometrial polyps are small, usually benign growths on the lining of the uterus. Like fibroids, they increase the surface area that sheds each month, and they can bleed between periods as well. Polyps are more common after age 40 and are typically discovered during an ultrasound. Cervical polyps can cause similar symptoms. In rare cases, heavy bleeding can signal precancerous or cancerous changes in the uterine lining, particularly in postmenopausal women or those with a long history of unopposed estrogen.
How to Tell If Your Periods Are Too Heavy
It’s hard to measure menstrual blood in milliliters at home, but there are practical benchmarks. You may have heavy menstrual bleeding if you’re soaking through one or more pads or tampons every hour for several consecutive hours, bleeding for more than 7 days, needing to change protection during the night, needing to wear two pads at once, or passing clots the size of a quarter or larger.
Doctors sometimes use a visual scoring system called a Pictorial Blood Loss Assessment Chart, where you track how saturated each pad or tampon is over the course of your period. Lightly stained items score low, fully soaked pads score highest, and clots add extra points. A total score above a certain threshold correlates with clinically heavy blood loss. Even without a formal chart, keeping a simple log of how many products you use and how saturated they are gives you and your doctor much better information than trying to describe it from memory.
When Heavy Periods Lead to Anemia
The most common complication of chronically heavy periods is iron deficiency anemia. Every period costs your body iron, and when blood loss outpaces what you can replace through diet, your iron stores gradually deplete. Early on, you might not notice much. As it progresses, symptoms include persistent fatigue, weakness, dizziness, shortness of breath with normal activity, and sometimes unusual cravings for ice or other non-food items.
Iron deficiency shows up on blood tests as low ferritin (your body’s stored iron) or low hemoglobin, or both. Many people with heavy periods assume their tiredness is just normal life, when it’s actually a treatable deficiency. If you’ve had heavy periods for months or years and feel constantly drained, checking your iron levels is a straightforward first step.