Blood clots during your period are usually normal. When your uterine lining sheds, your body releases natural anticoagulants to keep menstrual blood flowing smoothly. On heavier days, blood can leave the uterus faster than those anticoagulants can work, so some of it clots before exiting your body. Small clots, especially in the first day or two of your period, are extremely common and rarely a sign of any health problem.
That said, clot size and frequency do matter. Clots the size of a quarter or larger, or heavy clotting that happens every cycle, can point to an underlying condition worth investigating.
Normal Clots vs. Clots That Need Attention
Most period clots are small, dark red or maroon, and show up during the heaviest days of bleeding. They’re essentially bits of uterine lining mixed with blood that thickened before being passed. Clots smaller than a quarter (roughly 2.5 cm) that appear occasionally are generally nothing to worry about.
The CDC identifies clots the size of a quarter or larger as a sign of heavy menstrual bleeding. Other red flags include soaking through a pad or tampon every two hours or less, bleeding that lasts seven days or more, or bleeding so heavy it limits your daily activities. If your period consistently matches any of these patterns, something beyond normal shedding is likely driving the heavy flow.
Why Your Body Produces Clots
Your menstrual cycle is driven by two hormones working in sequence. Estrogen builds up the uterine lining during the first half of your cycle, thickening it in preparation for a potential pregnancy. After ovulation, progesterone stabilizes that lining. When pregnancy doesn’t occur, both hormones drop, and the lining sheds as your period.
Clotting becomes heavier when this process doesn’t go as planned. If you don’t ovulate in a given cycle, progesterone never kicks in, and estrogen keeps thickening the lining unopposed. The result is a much thicker lining that produces heavier bleeding and larger clots when it finally sheds. This is especially common during perimenopause, in people with polycystic ovary syndrome (PCOS), and in those with obesity, all situations where ovulation can become irregular.
Conditions That Cause Heavy Clotting
Fibroids and Polyps
Uterine fibroids are noncancerous growths in or on the uterus. They can distort the uterine cavity and increase the surface area of the lining, which means more tissue to shed and more blood flow each month. Polyps, smaller growths on the inner wall of the uterus, can have a similar effect. Both are common and treatable but can cause persistently heavy, clot-filled periods if left unaddressed.
Adenomyosis
In adenomyosis, 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. That misplaced tissue still responds to your hormones each month, bleeding and causing inflammation from within the muscle. Heavy menstrual bleeding with significant clotting and painful cramps are the two hallmark symptoms.
Endometriosis
Endometriosis involves uterine-like tissue growing outside the uterus, on the ovaries, fallopian tubes, or other pelvic organs. These growths respond to hormonal shifts just like your uterine lining, bleeding and breaking down each cycle. Because the blood has nowhere to exit, it causes inflammation, scarring, and adhesions. Both endometriosis and adenomyosis can cause intense menstrual pain alongside heavy bleeding, and they sometimes occur together.
Endometrial Hyperplasia
When the uterine lining grows excessively thick due to prolonged estrogen exposure without enough progesterone, the condition is called endometrial hyperplasia. The cells lining the uterus crowd together and can become abnormal. Bleeding that’s heavier or lasts longer than usual is the most common symptom. This condition is most frequently seen after menopause and during perimenopause, but it can develop anytime ovulation is irregular. Hyperplasia matters because, if untreated, it can progress to uterine cancer.
Bleeding Disorders
Some people with chronically heavy periods have an underlying bleeding disorder they’ve never been diagnosed with. Von Willebrand disease, the most common inherited bleeding disorder, affects the blood’s ability to clot properly throughout the body, not just during menstruation. Among women with heavy menstrual bleeding, between 5% and 24% are found to have von Willebrand disease. If you’ve had heavy periods since your very first cycle, bruise easily, or bleed heavily after dental work or minor injuries, a bleeding disorder may be contributing.
Could It Be a Miscarriage?
An early pregnancy loss can look very similar to a heavy period, especially if you didn’t know you were pregnant. Both involve cramping and passing clots. A few things set a miscarriage apart: the bleeding is often heavier than your typical period, cramping can be significantly more painful than what you normally experience, and you may pass tissue that looks different from your usual clots (grayish or lighter in color, sometimes with a recognizable sac-like shape).
If you’re sexually active and experience a period that’s unusually heavy, late, or accompanied by cramping far worse than normal, a pregnancy test or visit to your healthcare provider can clarify what’s happening. Soaking through two or more pads in an hour with severe symptoms warrants an emergency visit.
How Heavy Clotting Is Treated
Treatment depends entirely on what’s causing the heavy bleeding. For hormonal imbalances, hormonal birth control (pills, IUDs, or other methods) can regulate the cycle, thin the uterine lining, and dramatically reduce clotting. This is often the first approach for people without a structural cause like fibroids.
For people who prefer non-hormonal options, there are medications that work by preventing blood clots from breaking down too quickly, which reduces overall bleeding. These are typically taken only during the heaviest days of your period, up to five days per cycle.
Fibroids and polyps can sometimes be removed through minimally invasive procedures if they’re driving the problem. Adenomyosis is trickier to treat, but hormonal therapies can manage symptoms effectively for many people. In severe or resistant cases, surgical options exist.
For bleeding disorders like von Willebrand disease, treatment is tailored to the specific condition but often includes medications that improve clotting ability, sometimes alongside hormonal management to reduce menstrual flow.
Tracking What’s Normal for You
Period patterns vary enormously from person to person, so the most useful baseline is your own. Tracking your cycle length, how many days you bleed, how often you change pads or tampons, and the size of any clots gives you (and your doctor, if needed) concrete information to work with. A period that has always involved small clots on day two is very different from one that suddenly starts producing large clots after years of lighter flow.
Pay particular attention to changes. A gradual increase in clot size, cycles getting progressively heavier, or new pain accompanying your period are all patterns worth documenting. These shifts often signal that something in the uterus or hormone balance has changed, and catching it early makes treatment simpler.