Passing blood clots during your period is your body’s normal response to heavy menstrual flow, but when clots are frequent, large, or getting worse over time, something is usually driving your uterine lining to build up thicker than it should. Clots the size of a quarter or larger are considered abnormal by the CDC and worth investigating. The causes range from simple hormonal shifts to conditions like fibroids or bleeding disorders, and most are very treatable once identified.
How Period Clots Form
During your period, your body releases anticoagulants, natural blood-thinning substances that keep menstrual blood flowing smoothly. When bleeding is heavy or fast, your body can’t produce enough of these anticoagulants to keep up. The blood pools in your uterus or vagina, and your body’s normal clotting process kicks in, forming the jelly-like clumps you see on your pad or in the toilet.
Small clots, roughly the size of a pea or dime, during the heaviest day or two of your period are completely normal. What signals a problem is passing clots larger than a quarter, soaking through a pad or tampon every hour for several consecutive hours, or having periods that last longer than seven days. These patterns point to an underlying cause that’s making your uterine lining shed more tissue and blood than usual.
Hormonal Imbalance and a Thicker Lining
The most common reason for heavy, clot-filled periods is an imbalance between estrogen and progesterone. Estrogen builds up your uterine lining each cycle, thickening it in preparation for a possible pregnancy. After ovulation, progesterone rises and stabilizes that lining. If ovulation doesn’t happen, progesterone never kicks in, and estrogen keeps thickening the lining unopposed. When that overgrown lining finally sheds, there’s significantly more tissue and blood to pass, which means more clots.
This pattern is especially common during two life stages: the first few years of menstruation and the years leading up to menopause. Both are times when ovulation is irregular. But it can happen at any age due to conditions like polycystic ovary syndrome (PCOS), thyroid disorders, or significant weight changes. When the lining grows too thick, it’s called endometrial hyperplasia. The American College of Obstetricians and Gynecologists identifies excess estrogen without progesterone as the most common cause. Left untreated, the cells that make up the lining can crowd together and sometimes become abnormal, so persistent heavy bleeding is worth getting checked.
Fibroids and Adenomyosis
Uterine fibroids are noncancerous growths in or on the uterus, and they’re extremely common. By age 50, the majority of women have had at least one. Fibroids that grow into the uterine cavity or sit within the uterine wall distort the lining, increase its surface area, and interfere with the uterus’s ability to contract and stop bleeding. The result is heavier flow with more clotting. Fibroids can range from the size of a seed to a grapefruit, and the ones closest to the lining tend to cause the worst bleeding.
Adenomyosis is a related but distinct condition where tissue that normally lines the inside of the uterus grows into the muscular wall itself. That displaced tissue still responds to your hormones each cycle: it thickens, breaks down, and bleeds, but now it’s doing so inside the muscle. This makes the uterus enlarge and produces heavy, prolonged periods with significant clotting. Adenomyosis is most common in women in their 30s and 40s and often causes intense cramping alongside the heavy bleeding.
Bleeding Disorders
If you’ve had heavy, clotty periods since your very first cycle, a bleeding disorder is a real possibility that often goes undiagnosed for years. Von Willebrand disease, the most common inherited bleeding disorder, affects the blood’s ability to clot properly throughout your body, and heavy menstrual bleeding is frequently its most noticeable symptom.
Studies consistently find that 10 to 16 percent of women being evaluated for heavy menstrual bleeding turn out to have von Willebrand disease. That’s a substantial number. Other clues that a bleeding disorder might be involved include frequent nosebleeds, easy bruising, prolonged bleeding after dental work or surgery, or a family history of bleeding problems. If any of that sounds familiar alongside your heavy periods, it’s worth specifically requesting testing, since routine gynecological exams don’t automatically screen for it.
Other Contributing Factors
Copper IUDs (the non-hormonal type) are well known for making periods heavier and clottier, particularly in the first three to six months after insertion. This is one of the most straightforward causes: if your clotting started or worsened after getting a copper IUD placed, the device is the likely culprit.
Endometrial polyps, small overgrowths of the uterine lining, can also cause irregular or heavy bleeding with clots. Less commonly, certain medications that thin the blood, like aspirin or anticoagulants, can increase menstrual clotting. And in rare cases, heavy clotty periods can signal endometrial or cervical changes that need evaluation, which is why persistent symptoms deserve a proper workup.
Signs Your Body Is Losing Too Much Blood
Heavy periods with clots aren’t just an inconvenience. Over months or years, the blood loss adds up and can deplete your iron stores. Iron deficiency anemia is one of the most common consequences, and it develops so gradually that many women don’t realize it’s happening. Early on, you might not feel anything different at all.
As the deficiency worsens, symptoms creep in: deep fatigue that sleep doesn’t fix, shortness of breath during activities that used to feel easy, dizziness when standing up, cold hands and feet, pale skin, brittle nails, and a fast heartbeat. Headaches and restless legs at night are also common. If you’re experiencing several of these alongside heavy periods, your iron levels are likely low and a simple blood test can confirm it.
What Happens at a Doctor’s Visit
When you bring up heavy, clotty periods, your doctor will typically start with your menstrual history: how long your periods last, how often you’re changing pads or tampons, when the clotting started, and whether it’s gotten worse. Tracking your cycle with an app or calendar before your visit makes this conversation much more productive. You’ll also be asked about medications, birth control, pregnancy history, and symptoms of anemia or bleeding disorders.
Lab work usually includes a complete blood count to check for anemia, iron levels, thyroid function, and sometimes hormone levels or clotting tests. From there, imaging is the next step. An ultrasound is the standard first-line tool and can identify fibroids, polyps, and signs of adenomyosis. If more detail is needed, your doctor may recommend a sonohysterography (ultrasound with fluid placed in the uterus for a clearer picture), a hysteroscopy (a thin camera inserted through the cervix to directly view the inside of the uterus), or an endometrial biopsy to examine a tissue sample under a microscope. An MRI is sometimes used for a detailed look at internal structures.
How Heavy Clotting Is Treated
Treatment depends entirely on what’s causing the problem, which is why getting a diagnosis matters. For hormonal imbalances, hormonal birth control (pills, hormonal IUDs, or injections) is often the first approach because it regulates how thick the lining grows each cycle. A hormonal IUD in particular can dramatically reduce bleeding by keeping the lining thin.
For immediate symptom relief while a workup is underway, two medications are commonly used. Tranexamic acid, taken during your period, reduces bleeding by about 40 percent. It works by stabilizing clots once they form, preventing them from breaking down too quickly. NSAIDs like ibuprofen reduce bleeding by about 30 percent while also helping with cramping. Neither requires a long-term commitment: you take them only during your period.
Fibroids and polyps can often be removed through minimally invasive procedures, and adenomyosis may be managed with hormonal treatments or, in severe cases, surgery. For bleeding disorders like von Willebrand disease, targeted therapies can improve clotting function both during periods and in daily life. The key takeaway is that persistent heavy clotting isn’t something you simply have to live with. Nearly every cause has an effective treatment once it’s identified.