A period is considered heavy when you lose more than 80 mL of blood per cycle, which is roughly soaking through a regular pad or tampon every hour or two for several consecutive hours. If you’re changing protection constantly, passing large clots, or feeling drained by the end of your period, something is driving that extra blood loss. The causes range from hormonal shifts to structural changes in the uterus to blood clotting problems, and narrowing it down matters because the treatments are very different.
How to Tell If Your Flow Is Actually Heavy
Most people don’t measure their menstrual blood, so comparing yourself to a clinical threshold can feel abstract. A practical way to estimate: regular tampons absorb about 20 to 34 mL when fully soaked, and pads hold roughly 31 to 52 mL depending on the type. If you’re soaking through a super pad or tampon in under two hours, bleeding for more than seven days, or needing to double up (pad plus tampon), your flow likely exceeds that 80 mL mark.
Passing clots larger than a quarter, waking up at night to change protection, or feeling lightheaded and fatigued during your period are other reliable signals. These symptoms point to blood loss significant enough to affect your iron levels and daily functioning.
Hormonal Imbalance: The Most Common Cause
Your uterine lining builds up each cycle in response to estrogen. The thicker that lining grows, the more tissue has to shed, and the heavier your period will be. When estrogen runs high relative to progesterone (sometimes called estrogen dominance), the lining can grow excessively before your body sheds it.
This imbalance happens for several reasons. Irregular ovulation is one of the biggest. When you don’t ovulate in a given cycle, your body produces estrogen but very little progesterone, the hormone that normally keeps lining growth in check. The lining continues to thicken unchecked, and when it finally breaks down, the result is a heavier, often unpredictable bleed. Conditions like polycystic ovary syndrome, thyroid disorders, and significant weight changes can all disrupt ovulation and tip the hormonal balance toward heavier periods.
Fibroids and Polyps
Fibroids are noncancerous growths in the muscular wall of the uterus, and they’re extremely common. Not all fibroids cause heavy bleeding, but those that press into or distort the uterine cavity increase the surface area of the lining and interfere with the uterus’s ability to contract and stop bleeding after shedding. Fibroids that sit just beneath the lining (called submucosal fibroids) are the most likely to cause flooding-level periods.
Polyps are smaller, finger-like growths that form on the inner wall of the uterus when cells in the lining overgrow. They’re estrogen-sensitive, meaning they grow in response to estrogen circulating in your body. Even small polyps can cause heavy flow, irregular spotting between periods, or both. Both fibroids and polyps are typically found through ultrasound or a procedure where a tiny camera looks inside the uterus.
Adenomyosis
Adenomyosis is a condition where the tissue that normally lines the inside of the uterus starts growing into the muscular wall itself. During each cycle, that embedded tissue thickens, breaks down, and bleeds, just like the normal lining does. But because it’s trapped inside the muscle, it causes the uterus to enlarge and become boggy, which leads to significantly heavier and often more painful periods.
This condition is notoriously underdiagnosed because it doesn’t always show up clearly on a standard ultrasound. It’s most common in your 30s and 40s, and many people with adenomyosis describe their periods as getting progressively heavier over years, sometimes accompanied by deep, cramping pain that doesn’t respond well to typical painkillers.
Perimenopause and Life Stage Changes
If your periods have recently become heavier and you’re in your late 30s or 40s, perimenopause is a likely culprit. During this transition, estrogen and progesterone rise and fall unpredictably. You may skip ovulation some months, which lets the uterine lining build up longer than usual before shedding. The result can be cycles that alternate between light and shockingly heavy, sometimes with weeks of delay followed by a flood.
Teenagers in the first few years after their periods start can experience something similar. Their hormonal feedback loop isn’t fully mature yet, leading to irregular ovulation and occasionally very heavy cycles. At both ends of reproductive life, the underlying mechanism is the same: inconsistent ovulation disrupting the normal balance between estrogen and progesterone.
Bleeding Disorders
This is one of the most overlooked causes of heavy periods. A multicenter study of 200 adolescents with heavy menstrual bleeding found that 33% had an underlying bleeding disorder. The most common was low levels of von Willebrand factor, a protein that helps blood clot, affecting about 16% of those studied. Another 11% had von Willebrand disease itself, and about 4.5% had a platelet dysfunction.
If your periods have been heavy since they first started, you bruise easily, you bleed a long time after dental work or cuts, or you have a family history of bleeding problems, a clotting disorder is worth investigating. A simple set of blood tests can screen for most of these conditions, yet many people go years without being tested because heavy periods are often dismissed as normal variation.
IUDs, Medications, and Other Triggers
Copper IUDs are well known for increasing menstrual flow, particularly in the first three to six months after insertion. The copper creates a local inflammatory response in the uterus that can make periods heavier and crampier. Blood thinners, including daily aspirin, also increase menstrual blood loss because they reduce your blood’s ability to clot during shedding.
Hormonal IUDs, on the other hand, typically make periods lighter over time, so a sudden heavy flow while using one warrants a closer look. Other medications that can contribute include certain antidepressants and anti-inflammatory drugs taken regularly.
What Doctors Look For
Gynecologists use a classification system that organizes causes of heavy bleeding into nine categories: polyps, adenomyosis, fibroids, malignancy or precancerous overgrowth, clotting disorders, ovulatory dysfunction, problems with the lining itself, medication-related causes, and a catch-all for anything not yet classified. This framework helps systematically rule causes in or out rather than guessing.
A typical workup starts with blood tests to check your iron levels, thyroid function, and clotting ability. An ultrasound looks for structural issues like fibroids, polyps, or signs of adenomyosis. If those come back normal, the focus shifts to hormonal and ovulatory causes. In some cases, a biopsy of the uterine lining is done to rule out abnormal cell growth, especially if you’re over 45 or have risk factors.
Heavy periods aren’t something you just have to endure. Once the underlying cause is identified, treatment options range from hormonal approaches that thin the lining and reduce flow, to procedures that target fibroids or polyps directly, to addressing a clotting disorder with targeted therapy. The right approach depends entirely on what’s driving the bleeding, which is why getting a specific diagnosis matters more than treating the symptom alone.