Passing clots during your period is your body’s normal response to heavy menstrual flow, but frequent or large clots often signal that something is driving heavier-than-usual bleeding. Small clots (smaller than a quarter) on your heaviest days are common and not a concern on their own. Clots the size of a quarter or larger, or clots that keep coming throughout your period, point to an underlying cause worth investigating.
How Menstrual Clots Form
Your body produces natural anticoagulants to keep menstrual blood liquid as it leaves the uterus. When bleeding is heavy or fast, those anticoagulants can’t keep up, and the blood pools and clots before it exits. Think of it like a bottleneck: the more blood your uterus sheds, the more likely it is to clump together. The clots themselves are just thickened blood mixed with uterine lining tissue, which is why they can look dark red, maroon, or even grayish.
So the real question behind “why so many clots” is usually “why is my flow so heavy?” The clots are a symptom, not the root problem. The causes range from hormonal shifts to structural growths to conditions you may have had for years without knowing.
Hormonal Imbalances and a Thicker Lining
Estrogen builds up your uterine lining each cycle, and progesterone stabilizes it and triggers shedding. When estrogen runs high relative to progesterone, your lining keeps thickening beyond what’s typical. The result is more tissue to shed and a heavier, clottier period. This pattern is sometimes called “unopposed estrogen” because progesterone isn’t doing its usual counterbalancing job.
Over time, this imbalance can lead to endometrial hyperplasia, a condition where the uterine lining becomes abnormally thick. The most common symptom is heavy bleeding, often with clots. Hormonal imbalances like this are especially common during perimenopause (the years leading up to menopause), after significant weight changes, and in conditions like polycystic ovary syndrome where ovulation is irregular. When you don’t ovulate in a given cycle, your body doesn’t produce the progesterone surge that normally limits how thick the lining grows.
Fibroids and Polyps
Uterine fibroids are noncancerous growths in the muscular wall of the uterus, and they’re one of the most common structural causes of heavy, clotty periods. They increase bleeding through several mechanisms at once. A fibroid can enlarge the total surface area of the uterine lining, meaning there’s simply more tissue to bleed. It can also compress surrounding blood vessels, creating enlarged pools of blood (called venous lakes) within the uterine wall. The normal clotting process struggles to seal these dilated vessels, so bleeding continues longer and heavier than it should.
Fibroids also interfere with normal uterine contractions. Your uterus contracts during your period to help expel the lining and pinch off blood vessels. A fibroid sitting in the wall disrupts that squeezing action, allowing blood to flow more freely. On top of that, the blood vessels surrounding fibroids tend to be structurally fragile and prone to breaking open, adding to the volume of blood loss. Polyps, which are smaller growths on the inner lining of the uterus, cause similar problems on a smaller scale by creating extra surface area that bleeds.
Adenomyosis
Adenomyosis is a condition where the tissue that normally lines the inside of the uterus grows into the muscular wall. During your period, that embedded tissue also thickens, breaks down, and bleeds, just like the lining inside the uterus. This makes the uterus enlarge and bleed more heavily than normal. The hallmark symptoms are heavy, prolonged periods and significant cramping.
Adenomyosis frequently overlaps with fibroids and endometriosis, which can make it harder to pinpoint as the cause. Many people live with it for years before it’s identified, partly because the symptoms look so similar to other conditions. It’s most commonly diagnosed in people in their 30s and 40s, though it can occur earlier.
Bleeding Disorders
This is the cause most people don’t think to consider. A significant number of people with consistently heavy periods have an undiagnosed bleeding disorder. In a study of 200 adolescents with heavy menstrual bleeding, 33% were found to have a bleeding disorder. The most common was low levels of von Willebrand factor, a protein that helps blood clot, found in 16% of those studied. Another 11% had von Willebrand disease, and about 4.5% had problems with platelet function.
If you’ve had heavy, clotty periods since your very first cycle, or if you also bruise easily, bleed heavily after dental work, or have had excessive bleeding during or after surgery or childbirth, a bleeding disorder is worth ruling out. These conditions are treatable once identified, but they’re often missed because heavy periods get dismissed as “just how your body works.”
Could It Be a Miscarriage?
If your period is unusually late and then arrives with heavier-than-normal bleeding and larger clots, an early pregnancy loss is a possibility. Early miscarriage can look a lot like a very heavy period, especially in the first few weeks. The distinguishing signs tend to be cramping that’s significantly more painful than your typical period, bleeding that’s heavier than your heaviest normal day, and the disappearance of early pregnancy symptoms like breast tenderness or nausea. If you’re soaking through two or more pads in an hour, that warrants emergency care regardless of the cause.
What Doctors Look For
When you bring up heavy, clotty periods, the workup typically starts with your history. Your doctor will ask about how long your periods last, how heavy they are, and how long you’ve been experiencing clots. Periods lasting more than seven days and the presence of clots are both independent predictors of genuinely heavy menstrual bleeding, as opposed to periods that just feel heavy but fall within normal range.
A blood count checks whether you’ve become anemic from blood loss, and iron levels (specifically ferritin) reveal whether your body’s iron stores are depleted. The first imaging step is a transvaginal ultrasound, which can identify fibroids, polyps, and signs of adenomyosis. If the ultrasound is inconclusive, a saline infusion sonography (where fluid is used to expand the uterine cavity for a clearer view) or hysteroscopy (a tiny camera inserted through the cervix) may follow. Testing for bleeding disorders is typically reserved for cases where structural causes have been ruled out, or when your history suggests a clotting problem.
One thing that’s often not tested: thyroid function. Despite the common belief that thyroid problems cause heavy periods, research has never shown a clear relationship between thyroid function and heavy menstrual bleeding, so most guidelines don’t recommend thyroid testing as part of this workup.
Treatment Options
Treatment depends entirely on what’s causing the heavy bleeding, but there are several effective options across the spectrum.
For hormonal causes, oral progesterone can directly correct the estrogen-progesterone imbalance and reduce how thick your lining grows. Hormonal birth control pills regulate your cycle and lighten flow. A hormonal IUD that releases a small amount of progestin is one of the most effective options: it thins the uterine lining significantly and reduces both flow and cramping.
For immediate relief during heavy periods, ibuprofen and naproxen reduce menstrual blood loss (not just pain), and tranexamic acid is a non-hormonal medication taken only during bleeding days that helps your body’s clotting system work more effectively.
For fibroids specifically, newer medications that target the hormonal signals driving fibroid growth can control bleeding without surgery. When fibroids are large or causing significant symptoms, surgical removal of the fibroids (myomectomy) preserves the uterus. Endometrial ablation, which destroys the uterine lining, is an option for people who don’t plan future pregnancies. Hysterectomy remains the definitive treatment for severe cases of fibroids or adenomyosis when other approaches haven’t worked.
Clots That Signal a Problem
Small, occasional clots on your heaviest day or two are part of normal menstruation. The pattern to pay attention to is clots the size of a quarter or larger, clots that persist beyond your first couple of days, periods that last longer than seven days, or flow heavy enough that you’re soaking through a pad or tampon every hour for several consecutive hours. Fatigue, dizziness, and shortness of breath alongside heavy periods suggest you may already be anemic from chronic blood loss. Any of these patterns is a reason to get evaluated, because every cause on this list is treatable once it’s identified.