Heavy periods have a wide range of causes, from hormonal shifts to structural changes in the uterus to underlying bleeding disorders. Clinically, a period is considered heavy when you lose more than 80 milliliters of blood per cycle, but since no one measures that at home, the more practical signs matter: soaking through a pad or tampon every hour or two, passing clots the size of a quarter or larger, or bleeding for more than seven days. If any of that sounds familiar, something specific is driving it, and most causes are treatable once identified.
How to Tell If Your Bleeding Is Actually Heavy
It can be hard to know what “normal” looks like when you’ve only ever experienced your own cycle. The CDC considers these signs of heavy menstrual bleeding: needing to change your pad or tampon after less than two hours, doubling up on pads, waking at night to change protection, passing blood clots the size of a quarter or larger, periods lasting longer than seven days, or feeling tired, low-energy, or short of breath (a sign you may be losing enough blood to become anemic).
One tool doctors sometimes use is a pictorial blood assessment chart, which scores how saturated your pads or tampons are over the course of your period. A lightly stained pad scores 1 point, a moderately soaked one scores 5, and a fully saturated one scores 20. Tampons are scored similarly. A total score above a certain threshold (typically around 100) suggests genuinely heavy loss. You don’t need to use this formally, but paying attention to how quickly you soak through products and jotting it down for a few cycles gives your doctor something concrete to work with.
Hormonal Imbalance Is the Most Common Cause
Your period is essentially your body shedding the uterine lining it built up during the cycle. Estrogen builds that lining; progesterone keeps it in check. When there’s too much estrogen relative to progesterone, the lining grows thicker than it should, and the resulting period is heavier. This imbalance doesn’t mean something is broken. It can happen during perfectly ordinary life transitions.
Conditions that disrupt ovulation are a major driver. Polycystic ovary syndrome (PCOS), thyroid dysfunction, and hypothalamic disorders can all cause cycles where you don’t ovulate. Without ovulation, your body doesn’t produce the progesterone surge that normally limits lining growth. The lining keeps building under estrogen’s influence, and when it finally sheds, the bleeding is prolonged and heavy. Stress, significant weight changes, and extreme exercise can also interfere with ovulation in the same way.
Fibroids, Polyps, and Structural Changes
Fibroids are benign growths in the muscular wall of the uterus, and they’re remarkably common. They cause heavy bleeding through several overlapping mechanisms. As a fibroid grows, it increases the surface area of the uterine lining, giving you more tissue to shed. Fibroids also interfere with the uterus’s ability to contract properly after shedding, and those contractions are part of how your body slows bleeding at the end of a period.
At a deeper level, fibroids promote chaotic blood vessel formation in the surrounding tissue. These vessels are structurally fragile and prone to leaking. The fibroid also creates a surrounding capsule packed with blood vessels that can burst, and as the growth compresses nearby veins, it creates dilated pools of blood that are harder for normal clotting to seal off. Fibroids also release signaling molecules that reduce the lining’s natural clotting ability, compounding the problem. Not all fibroids cause symptoms. Location matters more than size: those growing into the uterine cavity (submucosal fibroids) are the most likely to cause heavy bleeding.
Endometrial polyps are smaller, finger-like growths on the lining itself. They can bleed between periods or make periods heavier. Like fibroids, most are benign, though they occasionally carry a small risk of precancerous changes.
Adenomyosis is a related condition where tissue that normally lines the uterus grows into the muscular wall. It often causes heavy, painful, prolonged periods along with an enlarged, tender uterus. It’s common in women in their 30s and 40s and is frequently underdiagnosed.
Life Stage Matters
Your age and reproductive stage have a significant effect on how heavy your periods are. Adolescents in the first few years of menstruation often have heavy, irregular cycles because their hormonal systems haven’t yet settled into a regular ovulatory pattern. Without consistent ovulation, the estrogen-progesterone balance tips toward heavier flow.
Perimenopause, the transition to menopause that typically begins in the early 40s, is one of the most common times for periods to suddenly become heavier or unpredictable. Ovarian function fluctuates, ovulation becomes inconsistent, and estrogen levels can spike relative to progesterone. Many women who never had period problems before experience flooding, prolonged bleeding, or cycles that arrive erratically during this phase. This can last for several years before periods stop entirely.
Bleeding Disorders Are More Common Than You’d Think
Heavy periods are sometimes the first and only sign of an underlying bleeding disorder. In a prospective U.S. study of 200 adolescents with heavy menstrual bleeding, a full 33% were diagnosed with a bleeding disorder. The most common was low levels of von Willebrand factor (16%), followed by von Willebrand disease (11%) and platelet dysfunction (about 5%).
Von Willebrand disease affects the blood’s ability to clot efficiently. If you’ve always had heavy periods starting from your very first one, bruise easily, bleed a long time after dental work or cuts, or have a family history of bleeding problems, a coagulation issue is worth investigating. It’s especially underrecognized in women because heavy periods are so often dismissed as “just how it is.”
Medications That Can Increase Flow
Certain medications cause or worsen heavy bleeding as a side effect. Blood thinners (anticoagulants) are the most obvious, but hormonal contraceptives can also be responsible, particularly copper IUDs, which are well known for making periods heavier in the first several months. Tamoxifen, used in breast cancer treatment, can trigger uterine bleeding as well. If your heavy periods started or worsened after beginning a new medication, that timing is worth noting.
What Happens When You Get It Checked
Doctors use a classification system called PALM-COEIN to systematically work through the possible causes. The “PALM” side covers structural problems: polyps, adenomyosis, leiomyomas (fibroids), and malignancy or precancerous overgrowth. The “COEIN” side covers non-structural causes: coagulopathy (bleeding disorders), ovulatory dysfunction, endometrial problems, medication-related (iatrogenic) causes, and other rare conditions like arteriovenous malformations or cesarean scar defects.
Evaluation typically starts with blood work to check for anemia, thyroid problems, and clotting issues, along with an ultrasound to look for fibroids, polyps, or other structural changes. Depending on your age and risk factors, the doctor may recommend an endometrial biopsy to rule out precancerous lining changes, particularly for women over 45 or those with prolonged irregular bleeding.
How Heavy Periods Are Treated
Treatment depends entirely on the cause. For hormonal imbalances and ovulatory dysfunction, hormonal options like birth control pills, hormonal IUDs, or cyclic progesterone can thin the lining and reduce flow significantly. A hormonal IUD in particular is one of the most effective treatments, often reducing bleeding by more than 90% over several months.
For women who can’t or prefer not to use hormones, a medication called tranexamic acid helps the blood clot more effectively within the uterus. Taken for four to five days starting on the first day of your period, it reduces menstrual blood loss by 26% to 60%. It doesn’t change your hormones or your cycle length; it simply reduces the volume of bleeding.
When fibroids or polyps are the cause, treatment ranges from medication to manage symptoms to procedures that remove the growths. The right approach depends on the size, number, and location of the growths, and whether you want to preserve fertility. Adenomyosis is trickier to treat because the tissue is embedded in the uterine wall, but hormonal IUDs and certain procedures can help.
For bleeding disorders, treatment focuses on the specific clotting problem. In some cases, the same hormonal or anti-bleeding medications used for other causes work well here too, but the underlying condition also needs ongoing management.
Signs That Need Prompt Attention
Soaking through one or more pads or tampons every hour for several consecutive hours is a situation that warrants urgent care. The same goes for feeling lightheaded, dizzy, or having a racing heartbeat alongside heavy bleeding, as these suggest significant blood loss. Passing large clots repeatedly, constant lower abdominal pain during your period, or being so fatigued and short of breath that you can’t function normally are all signals that your body is losing more blood than it can easily replace. Heavy periods that go untreated over time frequently lead to iron-deficiency anemia, which compounds the exhaustion and brain fog many women attribute to “just having a bad period.”