Clots during your period are clumps of blood that pass along with your menstrual flow, and in most cases they’re completely normal. They tend to show up on your heaviest days, often looking like dark red or maroon lumps ranging from the size of a pea to a small coin. As long as they’re smaller than a quarter, they’re generally nothing to worry about.
What Period Clots Actually Are
Despite the name, menstrual “clots” aren’t the same as the blood clots that form in veins or arteries. Standard blood clots are built from fibrin, a protein mesh your body creates to seal wounds. Menstrual clots contain no fibrin at all. They’re actually clumps of red blood cells held together by mucoid substances, mucoproteins, and glycogen. This is a meaningful distinction: your body isn’t malfunctioning by producing dangerous clots. It’s simply shedding tissue and blood faster than it can stay fully liquid.
During your period, the thickened lining of your uterus breaks down and exits your body as a mix of blood, tissue, and mucus. Your body produces natural anticoagulants to keep this discharge flowing smoothly. When bleeding is heavy or fast, those anticoagulants can’t keep up, and clumps form. Research shows that menstrual discharge actually has decreased levels of coagulation factors compared to regular blood, and fibrinogen (the precursor to fibrin) is entirely absent. Most of these clumps form in the vagina rather than inside the uterus itself, as blood pools there before being passed.
Normal Clots vs. Clots Worth Watching
Small clots on your heaviest days (usually days one through three) are a routine part of menstruation. They might look alarming, especially if they’re dark in color, but dark red, maroon, or even near-black clots simply reflect blood that took a bit longer to leave your body. The color has no medical significance on its own.
Size is the most practical way to gauge whether your clots fall outside the normal range. The CDC and the American College of Obstetricians and Gynecologists both use the same benchmark: clots the size of a quarter (about 2.5 centimeters across) or larger are a sign of heavy menstrual bleeding. A single large clot once in a while may not signal a problem, but if you’re regularly passing quarter-sized or larger clots, that pattern is worth investigating.
Other signs that your bleeding may be heavier than normal include:
- Soaking through a pad or tampon every hour for several hours in a row
- Needing to double up on pads
- Having to change pads or tampons overnight
- Periods lasting longer than seven days
Heavy menstrual bleeding affects roughly one in five women at some point. If any of these patterns describe your periods, the clots you’re seeing may be a symptom of something treatable rather than just a nuisance.
Why Some People Get More Clots
The most straightforward explanation is simply a heavier flow. The more blood your body sheds at once, the more likely it is to clump before passing. But when clotting is persistent and heavy, there’s often an underlying reason.
Fibroids
Uterine fibroids are noncancerous growths in or on the uterine wall. They’re extremely common, especially in the 30s and 40s, and they can distort the shape of the uterus or increase the surface area of the lining. Both of these changes mean more tissue to shed and more blood during each cycle, which leads to more clotting.
Adenomyosis
In adenomyosis, the tissue that normally lines the inside of the uterus grows into the muscular wall. During each cycle, this embedded tissue also thickens, breaks down, and bleeds, just like the regular lining does. The result is a uterus that may enlarge over time and periods that are heavier and more painful than they should be. Adenomyosis is a common cause of large clots and prolonged bleeding, particularly in women over 35.
Hormonal Imbalances
Your uterine lining thickens each month in response to estrogen, and progesterone helps regulate that growth. When the balance between these two hormones is off, the lining can build up more than usual, leading to a heavier shed and more clots when your period arrives. This type of imbalance is especially common during puberty, perimenopause, and in conditions like polycystic ovary syndrome (PCOS).
Other Causes
Copper intrauterine devices (IUDs) can increase menstrual flow, particularly in the first several months after placement. Bleeding disorders that affect how well your blood clots throughout the body, such as von Willebrand disease, can also cause heavier periods with more clotting. Endometrial polyps, small growths on the uterine lining, are another possibility.
How Heavy Bleeding and Clots Are Managed
Treatment depends entirely on what’s causing the heavy flow. If there’s no structural issue like fibroids, hormonal and non-hormonal medications are the typical first step.
Anti-inflammatory pain relievers like ibuprofen do more than ease cramps. They modestly reduce menstrual blood loss, which can mean fewer clots on heavy days. They work best when you start taking them at the beginning of your period rather than waiting until bleeding is heavy.
For more significant reduction in bleeding, a medication called tranexamic acid works by preventing the breakdown of clots your body forms naturally in the uterine blood vessels. It’s taken as a tablet on your heaviest days, up to five days per cycle. Cochrane review data shows it’s more effective at reducing heavy menstrual bleeding than anti-inflammatory painkillers alone.
Hormonal options, including birth control pills, hormonal IUDs, and other progesterone-based treatments, work by thinning the uterine lining so there’s less to shed each month. A hormonal IUD is one of the most effective options, often reducing flow dramatically within a few months. For fibroids or adenomyosis causing severe symptoms, procedures ranging from minimally invasive techniques to surgery may be recommended depending on the size, location, and your plans for future pregnancies.
When Clots Change Suddenly
If your periods have always included small clots and nothing else has changed, that’s your normal. What matters more than any single clot is a shift in your pattern. Clots that are suddenly much larger than usual, periods that are getting progressively heavier over several months, or new symptoms like fatigue, dizziness, or shortness of breath (all signs of iron-deficiency anemia from chronic blood loss) are signals that something has changed and is worth looking into. Anemia from heavy periods develops gradually, so many people adapt to feeling tired without connecting it to their cycle.
Tracking your period for a few months, including how often you change protection, whether you pass clots, and roughly how large they are, gives you concrete information to share if you do seek care. It turns a vague concern into something measurable.