A sudden increase in menstrual bleeding usually signals a shift in your hormones, a new structural change in your uterus, or sometimes a medication you recently started. Clinically, a “heavy” period means losing more than 80 milliliters of blood per cycle, though only about 40 to 50 percent of women who feel their periods are heavy actually exceed that threshold. The more practical measure: soaking through a pad or tampon every hour for several consecutive hours, passing clots larger than a quarter, or bleeding that lasts beyond seven days.
Several conditions can flip the switch from normal to heavy seemingly overnight. Some are harmless and temporary. Others need attention. Here’s what could be behind the change.
Hormonal Shifts and Anovulatory Cycles
The most common reason for a suddenly heavier period is a hormonal imbalance, specifically too much estrogen relative to progesterone. During a normal cycle, estrogen thickens your uterine lining in the first half, and progesterone stabilizes it in the second half after ovulation. If you don’t ovulate in a given cycle (called an anovulatory cycle), progesterone never rises enough to keep that lining in check. Estrogen continues building the lining unopposed, and when it finally sheds, the result is a heavier, often longer bleed.
Anovulatory cycles can happen to anyone occasionally, but they’re especially common during two life stages: the first few years after your period starts and the years leading up to menopause. Stress, rapid weight changes, thyroid problems, and polycystic ovary syndrome (PCOS) can also disrupt ovulation and tip the balance toward estrogen dominance. When this imbalance becomes chronic, it can cause a condition called endometrial hyperplasia, where the lining grows excessively thick and produces prolonged, heavy bleeding.
Fibroids and Polyps
Uterine fibroids are noncancerous growths in or on the uterine wall. They can develop slowly for years without symptoms, then reach a size or position where they suddenly affect your bleeding. Fibroids that grow within the uterine muscle (intramural fibroids) are surrounded by a dense network of blood vessels that feed the growth. These vessels form chaotically, much like the disorganized blood supply around a tumor, making them fragile and prone to breaking. The result is heavy, sometimes unpredictable bleeding.
Fibroids can also physically compress nearby veins, creating enlarged pools of blood within the uterine lining that release during your period. The severity of bleeding tends to correlate with where the fibroid sits: those pressing into the uterine cavity cause the most trouble. Endometrial polyps, which are smaller finger-like growths on the lining itself, work differently but produce a similar effect. They add extra surface area of fragile tissue that bleeds easily. Both fibroids and polyps are common, and both can appear or grow quickly enough to make a period noticeably heavier from one cycle to the next.
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 double or triple its normal size. The hallmark symptoms are heavy menstrual bleeding with clotting, severe cramps, and pelvic pain that may also flare during sex.
About one in three people with adenomyosis have no symptoms at all, which means the condition can progress silently before reaching a tipping point where bleeding becomes dramatically heavier. Diagnosis typically involves a pelvic exam (your provider may notice a larger, softer, or tender uterus) and a transvaginal ultrasound. Because adenomyosis increases your risk of anemia from blood loss, it’s worth investigating if your periods have become both heavier and more painful.
Perimenopause
If you’re in your 40s or early 50s and your period just got noticeably heavier, perimenopause is a likely explanation. The average age of menopause in developed countries is 51, but the hormonal transition can begin a full decade earlier. During this window, ovulation becomes unpredictable. Some cycles produce normal progesterone, others produce very little, and the fluctuation leads to periods that vary wildly in flow and timing.
Heavy bleeding is one of the most common perimenopausal symptoms, particularly for women aged 40 to 54. The pattern often includes heavier flow alongside cycles that are shorter, longer, or irregularly spaced. Research shows a strong link between skipped periods and the eventual resolution of heavy bleeding in women over 45. Women who begin skipping periods are two to five times more likely to see their heavy bleeding resolve on its own compared to those with regular cycles. So while the heavy phase can feel alarming, it’s often a signal that your body is moving toward menopause rather than away from health.
Medications and Supplements
A change in medication is one of the most overlooked causes of sudden heavy periods. Blood thinners like warfarin and heparin directly interfere with your body’s clotting ability, which can make menstrual bleeding significantly heavier. Common over-the-counter pain relievers like aspirin and ibuprofen also have mild blood-thinning effects, and taking them regularly around your period can increase flow.
Certain herbal supplements carry similar risks. Ginkgo biloba can promote bleeding on its own and becomes riskier when combined with aspirin or other anti-inflammatory drugs. Garlic supplements amplify the blood-thinning effects of both aspirin and warfarin. Evening primrose oil has been reported to increase bleeding when taken alongside medications that slow clotting. If you recently started any new supplement or medication and noticed your period getting heavier, that connection is worth exploring with your provider.
Hormonal IUDs and birth control changes can also shift your bleeding pattern. Copper IUDs, in particular, are well known for making periods heavier, especially in the first several months after insertion.
Bleeding Disorders
Sometimes heavy periods aren’t caused by anything in the uterus at all. Von Willebrand disease (VWD) is the most common inherited bleeding disorder, affecting up to 1 percent of the population. It impairs your blood’s ability to clot properly. Women are disproportionately affected because menstruation puts the disorder on full display: in CDC studies, 93 to 95 percent of women with VWD reported heavy menstrual bleeding as a symptom.
VWD is notoriously underdiagnosed. Women in a CDC survey reported an average of six different bleeding symptoms before finally receiving a diagnosis, and testing had to be repeated an average of two times (and up to 20) to confirm it. Other signs that a bleeding disorder might be behind your heavy periods include easy bruising, frequent nosebleeds, prolonged bleeding after dental work or minor injuries, and excessive bleeding during childbirth. If these sound familiar and your periods have always been on the heavier side (or have recently become much worse), a blood test can check for VWD and other clotting problems.
Early Miscarriage
A period that arrives late and then hits unusually hard, especially with large clots and cramping, may actually be an early miscarriage. Most miscarriages occur within the first 13 weeks of pregnancy, and very early losses (before you even knew you were pregnant) can easily be mistaken for a heavy, late period. The bleeding may be accompanied by cramping pain, and the flow is often heavier and more prolonged than a typical period.
If heavy bleeding comes with a fast heartbeat, dizziness, or significant weakness, that suggests more serious blood loss and warrants immediate medical attention.
Signs of Anemia From Blood Loss
Regardless of the cause, repeatedly heavy periods can drain your iron stores and lead to iron deficiency anemia. This doesn’t always happen after one bad cycle, but if your periods have been heavy for several months, watch for: extreme tiredness that rest doesn’t fix, pale skin, shortness of breath with normal activity, cold hands and feet, headaches or dizziness, brittle nails, and restless legs at night.
One of the more unusual signs of iron deficiency is pica, a craving for non-food items like ice, dirt, or clay. Craving and chewing ice constantly is a surprisingly specific red flag. If you’re experiencing several of these symptoms alongside heavy periods, a simple blood test can check your iron levels and hemoglobin. Iron deficiency from heavy periods is very treatable, but it won’t resolve on its own if the underlying bleeding continues.