Passing small blood clots during your period is normal, and most people experience them at some point. Clots up to about the size of a quarter are typical, especially on your heaviest days. But if you’re regularly passing clots larger than that, or soaking through pads and tampons every hour or two, something beyond normal menstruation is likely going on. Several common conditions can increase both the volume of your flow and the size of the clots you pass.
How Period Clots Actually Form
Period clots aren’t the same kind of clots that form in a blood vessel. They’re actually clumps of red blood cells held together by mucous-like proteins and other substances, and they tend to form in the vagina rather than inside the uterus itself. Your body produces enzymes that work to break down menstrual blood and keep it fluid so it can exit easily. When bleeding is light or moderate, those enzymes generally keep up. On heavier days, blood can pool and sit long enough in the vagina to clump together before it passes, which is why you tend to see more clots in the first day or two of your period or after lying down overnight.
When flow is consistently heavy, the body’s clot-dissolving system gets overwhelmed. The result is larger, more frequent clots. So the question isn’t really “why do I have clots” but rather “why is my flow heavy enough to produce so many of them?”
Uterine Fibroids
Fibroids are noncancerous growths in or on the uterus, and they’re one of the most common reasons for heavy periods with clots. They’re especially prevalent in people over 30, though they can develop earlier. The location of a fibroid matters more than the size. Fibroids that press into the uterine lining distort its surface area, which means more tissue builds up each cycle and more blood is shed when it breaks down.
Fibroids can also interfere with the uterus’s ability to contract. Normally, the uterus squeezes down during your period to help control bleeding, similar to how it contracts after childbirth. When fibroids get in the way, the uterus can’t clamp down effectively, so bleeding is heavier and lasts longer. Chemical signals called prostaglandins, which regulate uterine contractions, can also be thrown off by fibroids, compounding the problem.
Adenomyosis
Adenomyosis happens when tissue that normally lines the inside of the uterus starts growing into the muscular wall. This thickens the uterine wall and often enlarges the entire uterus. Because this embedded tissue still responds to your hormones each month, it swells, bleeds, and causes inflammation trapped within the muscle itself. The result is heavy menstrual bleeding paired with intense, deep cramping that can feel different from typical period pain.
Adenomyosis is frequently misdiagnosed or overlooked because its symptoms overlap with fibroids and endometriosis. It’s most commonly diagnosed in people in their 30s and 40s, though it can occur earlier. If your periods have gradually become heavier and more painful over the years, adenomyosis is worth investigating.
Endometriosis
Endometriosis involves tissue similar to the uterine lining growing outside the uterus, on organs like the ovaries, fallopian tubes, or bowel. These growths respond to hormonal shifts just like the tissue inside your uterus, bleeding and breaking down each cycle. But unlike a normal period, that blood has no way to exit the body, so it causes inflammation, scarring, and adhesions. Heavy periods with clots can be part of the picture, though endometriosis is more closely associated with severe pelvic pain, pain during sex, and pain with bowel movements.
Hormonal Imbalances
Your period is regulated by a balance between estrogen and progesterone. Estrogen builds up the uterine lining during the first half of your cycle, and progesterone stabilizes it after ovulation. If you produce too much estrogen relative to progesterone, the lining grows thicker than it should. When it finally sheds, there’s simply more material to pass, leading to heavier flow and more clots.
This imbalance can happen for several reasons. Irregular ovulation is one of the most common. If you don’t ovulate in a given cycle, your body doesn’t produce the progesterone surge that would normally keep the lining in check. The lining keeps thickening under estrogen’s influence until it becomes unstable and sheds unevenly. Conditions like polycystic ovary syndrome, thyroid disorders, and perimenopause all increase the likelihood of anovulatory cycles. Over time, persistent estrogen dominance can lead to a condition called endometrial hyperplasia, where the uterine lining becomes abnormally thick and causes heavy or irregular bleeding.
Bleeding Disorders
Sometimes heavy periods with frequent clots point to a problem with how your blood clots throughout your body, not just during menstruation. Von Willebrand disease is the most common inherited bleeding disorder, and it disproportionately affects people who menstruate. Among those with chronically heavy periods, between 5% and 24% turn out to have von Willebrand disease. It’s more prevalent in white women (about 16%) than in Black women (around 1%).
If you’ve had heavy periods since your very first cycle, bruise easily, bleed heavily after dental work or minor injuries, or have a family history of bleeding problems, a bleeding disorder is worth screening for. It’s one of the more frequently missed causes because many people assume heavy periods are just “their normal.”
How Heavy Is Too Heavy
It can be hard to gauge what counts as abnormally heavy when you’ve never had a reference point. These are signs that your bleeding has crossed into territory that warrants medical attention:
- Clot size and frequency: Passing clots larger than a quarter more than once or twice during a period.
- Pad or tampon use: Soaking through a pad or tampon every one to two hours for several hours in a row, or needing to double up on protection.
- Nighttime disruption: Regularly needing to wake up to change a pad or tampon overnight.
- Duration: Periods lasting longer than seven days.
- Volume: Losing more than about 5 tablespoons of blood per period (the average is 2 to 3 tablespoons, though this is hard to measure precisely).
If you’re soaking through two or more pads or tampons per hour for two to three hours straight, that’s a sign to seek care urgently rather than waiting for a scheduled appointment.
The Anemia Connection
Chronically heavy periods are one of the leading causes of iron deficiency anemia, and many people don’t connect their symptoms to their period. The blood loss depletes your iron stores gradually, so you may not notice a dramatic shift. Instead, you might feel persistently tired, weak, or short of breath with activity you used to handle easily. Pale skin, cold hands and feet, dizziness, headaches, brittle nails, and restless legs at night are all common signs. Some people develop unusual cravings for ice, dirt, or non-food items, which is a hallmark of significant iron deficiency.
If any of these symptoms sound familiar alongside heavy, clotty periods, a simple blood test can check your iron levels and blood count. Treating the anemia with iron is straightforward, but it won’t solve the problem long-term unless the underlying cause of the heavy bleeding is also addressed.
Treatment Options That Reduce Clots
Treatment depends on what’s driving the heavy bleeding, but several options specifically target the volume of flow and clot formation. Hormonal approaches, including birth control pills, hormonal IUDs, and other progesterone-based treatments, work by thinning the uterine lining so there’s less tissue to shed each month. For many people, a hormonal IUD dramatically reduces both flow and clots over the first few months of use.
For those who prefer non-hormonal treatment, there’s a medication that works by blocking the enzymes that dissolve clots in menstrual fluid. In clinical studies, it reduced menstrual blood loss by 40% to 65%, and about 80% of women reported improved quality of life by the third cycle of use. It’s taken only during the days of your period, not continuously.
When fibroids or adenomyosis are the cause, treatment may involve procedures to remove the fibroids, reduce the uterine lining, or in more severe cases, surgery. The right approach depends on the size and location of growths, symptom severity, and whether you want to preserve fertility.