Many things can make your period heavier, from hormonal shifts and structural changes in the uterus to underlying medical conditions and certain medications. Clinically, heavy menstrual bleeding is defined as losing more than 80 mL of blood per cycle, but in practical terms, it means soaking through a pad or tampon every hour or two, passing large clots, or bleeding for more than seven days. Understanding what’s behind the change can help you figure out whether it’s temporary or something worth investigating.
Hormonal Imbalance
The most common driver of heavier periods is a mismatch between estrogen and progesterone, the two hormones that control your uterine lining. Estrogen builds the lining up each cycle. Progesterone, released after ovulation, stabilizes it and signals it to shed in an orderly way. When estrogen runs high without enough progesterone to counterbalance it, the lining keeps thickening beyond what’s normal. The result is a heavier, longer bleed when it finally breaks down.
This imbalance can happen for several reasons. Polycystic ovary syndrome (PCOS) is one of the most common. In PCOS, ovulation doesn’t happen regularly, which means the corpus luteum (the structure that produces progesterone after an egg is released) never forms. Without that progesterone, the lining stays in a constant growth phase. It becomes unstable and eventually sheds irregularly, often with significantly more blood. High estrogen levels without progesterone also increase vascular fragility in the lining itself, so the blood vessels bleed more freely.
Perimenopause is another major trigger. In the years leading up to menopause, estrogen levels swing unpredictably, sometimes surging higher than normal before dropping. Ovulation becomes unreliable, so progesterone production is inconsistent. This creates cycles where your period might be light one month and unusually heavy the next, or you might skip a period entirely and then have a prolonged, heavy bleed.
Fibroids and Polyps
Uterine fibroids are noncancerous growths in or on the uterine wall, and they’re one of the most common structural causes of heavy periods. They increase bleeding through several mechanisms. Fibroids that grow near or into the uterine cavity expand the surface area of the lining, giving it more tissue to shed. They also interfere with the uterus’s ability to contract properly during your period. Those contractions are what helps pinch off blood vessels and slow bleeding, so when fibroids disrupt them, blood flow increases.
Fibroids also cause physical changes to blood flow within the uterine wall. As they grow, they compress surrounding veins and create enlarged pools of blood, sometimes called venous lakes. These dilated vessels, formed by the pressure the fibroids exert on surrounding tissue, contribute to heavier flow. The fibroids also promote the growth of abnormal blood vessel networks around them, which adds to the problem.
Uterine polyps work differently but produce a similar effect. These small, soft growths on the uterine lining have their own blood supply and can bleed between periods or make your regular period heavier. Unlike fibroids, polyps are usually small and confined to the lining itself.
Adenomyosis
Adenomyosis happens when tissue that normally lines the uterus grows into the muscular wall of the uterus itself. This causes the uterine wall to thicken and the uterus to enlarge, sometimes to two or three times its normal size. It’s a common condition, particularly in women in their 30s and 40s, and it reliably causes both heavier periods and more painful cramping.
The embedded tissue triggers a cascade of inflammation within the muscle wall. That inflammation stimulates the growth of new blood vessels (increasing the blood supply to the area) and disrupts normal uterine contractions. Both of these changes increase menstrual blood loss. The inflammation also promotes the growth of new nerve fibers in the uterine wall, which is why adenomyosis tends to cause intense, deep cramping alongside the heavy flow.
Thyroid Problems
An underactive thyroid can make your periods noticeably heavier, and this connection is frequently overlooked. Low thyroid hormone levels affect your body’s clotting system, shifting it toward a state where blood doesn’t clot as efficiently. One of the most significant effects is a drop in von Willebrand factor, a protein essential for clot formation. This creates a temporary bleeding disorder that resolves once thyroid levels are corrected with medication.
Hypothyroidism also disrupts the hormonal signals between your brain and ovaries. The thyroid axis and the reproductive hormone axis are closely linked, so when thyroid function drops, it can alter levels of sex hormones, interfere with ovulation, and raise prolactin levels. All of these changes can independently contribute to heavier or more irregular bleeding.
Bleeding Disorders
Some people have always had heavy periods and assume it’s just how their body works, when in fact an inherited bleeding disorder is the cause. Von Willebrand disease is the most common one, and heavy menstrual bleeding is its most frequently reported symptom. In studies of women with von Willebrand disease, 93 to 95% report heavy periods. Other clotting factor deficiencies and platelet disorders can produce the same effect.
Bleeding disorders are worth considering if your periods have been heavy since they first started, especially if you also bruise easily, bleed a lot from dental work or minor cuts, or have a family history of bleeding problems. These conditions are underdiagnosed in women because heavy periods are often dismissed as normal variation.
The Copper IUD
If your periods got heavier after getting a non-hormonal (copper) IUD, that’s a well-documented side effect. Research using measured menstrual blood loss shows that copper IUDs increase flow by about 50% over pre-insertion levels, and this increase appears to stay relatively constant for at least the first 12 months. In one study of over 600 users, 60% reported increases in flow over a 12-month period.
The copper itself triggers a local inflammatory response in the uterine lining, which is part of how the device prevents pregnancy but also why it causes heavier bleeding. Hormonal IUDs, by contrast, typically reduce menstrual flow significantly.
Medications That Increase Bleeding
Blood-thinning medications, including both prescription anticoagulants and common over-the-counter pain relievers like aspirin and ibuprofen, can increase menstrual flow. Anticoagulants reduce the blood’s ability to clot throughout your body, and that includes the blood vessels in your uterine lining during your period. If you’ve started a blood thinner and noticed heavier periods, the connection is likely direct.
Aspirin and similar anti-inflammatory drugs inhibit platelet function, which makes them a particular concern for anyone who already has a bleeding disorder or borderline-heavy periods. While ibuprofen is actually used to reduce flow in many women (it works on the inflammatory pathways that drive bleeding), its effect on platelet clumping means it can worsen bleeding in some situations.
When Heavy Periods Cause Anemia
The most significant health consequence of chronically heavy periods is iron deficiency anemia. Every period depletes your iron stores, and when the loss consistently exceeds what you take in through food, your reserves drop. This happens in stages. First, your stored iron (measured as ferritin) falls below 30 ng/mL, even while your blood counts look normal. You might feel more tired than usual but have no obvious explanation. In the next stage, your body can’t make red blood cells efficiently, and your iron levels in the blood drop below normal. By the third stage, your red blood cells become smaller and paler than they should be, and symptoms like fatigue, shortness of breath, dizziness, and brain fog become hard to ignore.
If your periods have been heavy for months or years, checking your ferritin level is more useful than a standard blood count alone. Ferritin drops long before your hemoglobin does, so it catches the problem earlier. Normal ferritin ranges start at 30 ng/mL, and many women with heavy periods fall well below that without realizing their fatigue has a treatable cause.