A heavy period has many possible causes, ranging from hormonal imbalances and structural growths in the uterus to thyroid problems and bleeding disorders. Clinically, a period is considered heavy when you lose more than 80 milliliters of blood per cycle, roughly equivalent to soaking through a pad or tampon every hour for several consecutive hours. About one in five women experience heavy periods, and while that’s common, it’s not something you need to just live with.
How to Tell If Your Flow Is Actually Heavy
Most people don’t measure their menstrual blood in milliliters, so the clinical threshold isn’t always helpful on its own. In practical terms, your period is likely heavier than normal if you’re soaking through a pad or tampon every one to two hours, passing blood clots larger than a quarter, bleeding for more than seven days, or doubling up on protection (a pad plus a tampon). Waking up at night to change your pad is another reliable signal.
One consequence that often gets overlooked is iron deficiency. Chronic heavy bleeding drains your iron stores over time, and you’re considered iron deficient when your ferritin level drops below 30 ng/mL. If you’ve been feeling unusually tired, short of breath during normal activity, or foggy-headed, low iron from heavy periods could be the reason. A simple blood test can check this.
Hormonal Imbalances and Missed Ovulation
The most common hormonal cause of heavy periods is anovulation, meaning your body doesn’t release an egg during a cycle. When ovulation doesn’t happen, you don’t produce progesterone, the hormone that normally stops the uterine lining from growing too thick. Without it, estrogen keeps building up that lining unchecked. Eventually the lining becomes unstable and sheds unevenly, often producing prolonged, heavy, or unpredictable bleeding.
Polycystic ovary syndrome (PCOS) is a well-known driver of this pattern. In women with PCOS who aren’t on hormonal birth control or periodic progesterone, about 35% develop a thickened uterine lining (endometrial hyperplasia) as a direct result of this unopposed estrogen. Anovulatory cycles are also common during puberty, the years leading up to menopause, and periods of significant stress or weight change. If your periods are irregular and heavy, a hormonal imbalance is one of the first things worth investigating.
Fibroids, Polyps, and Adenomyosis
Structural changes inside the uterus are another major category. Uterine fibroids are noncancerous muscle growths in the uterine wall that can distort the shape of the cavity, increase its surface area, and interfere with the uterus’s ability to contract and stop bleeding. Not all fibroids cause heavy periods. The ones most likely to affect your flow are those growing into the inner cavity of the uterus, called submucosal fibroids.
Uterine polyps are softer growths that form when cells in the uterine lining overgrow. They attach to the uterine wall by either a broad base or a thin stalk and can cause heavy flow, irregular spotting, or bleeding between periods. Polyps are usually small but can grow large enough to fill part of the uterine cavity.
Adenomyosis is a condition where tissue that normally lines the uterus begins growing into the muscular wall instead. This causes the uterus to become enlarged and tender, and it typically produces both heavy bleeding and severe cramping. It’s sometimes confused with endometriosis, which involves similar tissue growing outside the uterus. The key difference is location: adenomyosis stays within the uterine wall itself, while endometriosis affects other organs and tends to cause more varied pain depending on where the growths are. Both conditions can exist at the same time.
Thyroid Problems
An underactive thyroid can make periods heavier through several overlapping mechanisms. Low thyroid hormone disrupts the chain of signals between your brain and ovaries, which can suppress ovulation and leave estrogen unopposed, the same pattern described above. Thyroid-stimulating hormone (TSH), which rises sharply when the thyroid is underperforming, can also trigger excess prolactin production, further disrupting the hormonal signals that regulate your cycle.
Beyond hormones, hypothyroidism affects your blood’s ability to clot. It can cause platelet dysfunction and shift your body into a state where clotting is less efficient, meaning the uterus bleeds more freely during a period. This combination of impaired clotting and hormonal disruption explains why heavy periods are sometimes the first noticeable symptom of a thyroid problem, even before fatigue or weight gain become obvious.
Bleeding Disorders
Some women have heavy periods their entire lives and assume it’s just how their body works, when the real cause is an underlying bleeding disorder. Von Willebrand disease, the most common inherited bleeding condition, affects how well your blood forms clots. Among women with chronic heavy menstrual bleeding, somewhere between 5% and 24% test positive for Von Willebrand disease or another clotting disorder. That’s a significant number.
Clues that a bleeding disorder might be involved include heavy periods starting from your very first cycle, a history of easy bruising, prolonged bleeding after dental work or surgery, or a family member with a known bleeding condition. These disorders are underdiagnosed in women partly because heavy periods are so often dismissed as normal.
The Copper IUD and Other Medications
If your periods became heavy after getting a copper IUD, the device itself is likely the cause. Studies show menstrual blood loss increases by about 50 to 55% after copper IUD insertion, jumping from an average of 59 mL to 91 mL per cycle. This increase tends to appear within the first three months and then levels off. For most women the extra bleeding doesn’t cause significant anemia, but if you were already on the heavier side before insertion, it can push you past a comfortable threshold.
Blood thinners (anticoagulants) are another common medication-related cause. Certain anti-inflammatory drugs, hormone therapies, and herbal supplements that affect clotting can also increase flow. If the timing of your heavier periods lines up with starting a new medication, that connection is worth exploring.
What Happens During Evaluation
Doctors typically organize the causes of heavy bleeding into two broad groups: structural problems you can see on imaging (polyps, adenomyosis, fibroids, and rarely malignancy) and non-structural causes (clotting disorders, ovulatory dysfunction, medication effects, and endometrial issues). An evaluation usually starts with blood work to check your blood count, iron levels, thyroid function, and sometimes clotting factors, followed by an ultrasound to look for structural abnormalities inside the uterus.
If the ultrasound doesn’t reveal a clear cause, further steps might include a saline-infused sonogram for a better view of the uterine cavity or a small biopsy of the lining. The goal is to match your specific pattern of bleeding to one of these categories so treatment can target the actual cause rather than just manage symptoms.
How Heavy Periods Are Treated
Treatment depends entirely on the underlying cause, but several options can reduce flow significantly. Hormonal approaches, including birth control pills, hormonal IUDs, and cyclic progesterone, work by thinning the uterine lining or regulating ovulation. A hormonal IUD is one of the most effective options, reducing flow by up to 90% for many women.
For women who prefer a non-hormonal option, tranexamic acid is a medication taken only during your period that helps blood clot more effectively in the uterus. In clinical trials, it reduced menstrual blood loss by about 40% compared to roughly 8% with a placebo. It doesn’t affect your cycle’s timing or hormones.
When fibroids or polyps are the cause, removing them often resolves the heavy bleeding directly. Adenomyosis is harder to treat surgically without removing the uterus, so it’s usually managed with hormonal options first. For bleeding disorders like Von Willebrand disease, targeted treatments that boost clotting factors can make a dramatic difference in flow.