A period that’s suddenly heavier than normal usually signals a shift in your hormones, though it can also point to structural changes in your uterus or, less commonly, an underlying health condition. Clinically, a period is considered heavy when you lose more than 80 mL of blood per cycle, which roughly translates to soaking through a pad or tampon every two hours or less. But you don’t need to measure your blood loss to know something has changed. If your flow feels noticeably different from your personal baseline, that’s worth paying attention to.
Hormonal Shifts Are the Most Common Cause
Your menstrual flow is directly tied to how thick your uterine lining grows each cycle, and that thickness is controlled by two hormones: estrogen and progesterone. During the first half of your cycle, estrogen builds up the lining. After ovulation, progesterone stabilizes it and triggers a controlled shed when pregnancy doesn’t occur. When this balance tips, especially when estrogen runs high relative to progesterone, the lining grows thicker than usual and produces a heavier bleed.
The most common reason for this imbalance is an anovulatory cycle, meaning a cycle where your body doesn’t release an egg. Without ovulation, your ovaries don’t produce progesterone, so estrogen continues thickening the lining unopposed. The result is a period that arrives late and comes on heavy, often with large clots. Anovulatory cycles can happen to anyone occasionally, but they become more frequent during certain life stages and in conditions like polycystic ovary syndrome (PCOS) or thyroid disorders.
Stress, rapid weight changes, intense exercise, and illness can all disrupt ovulation for a cycle or two, causing a one-off heavy period that resolves on its own.
Perimenopause and Age-Related Changes
If you’re in your late 30s or 40s, heavier periods are extremely common. During perimenopause, which can begin up to 10 years before your final period, your cycles become less predictable. Both unusually short cycles (under 21 days) and long cycles (over 36 days) are associated with anovulatory patterns, and those anovulatory cycles tend to produce heavier, more erratic bleeding. You might go a couple of months with lighter flow, then get hit with a period that’s dramatically heavier than anything you’ve experienced.
This happens because your ovaries are producing estrogen less consistently but haven’t stopped entirely. The fluctuations create cycles where estrogen builds the lining for weeks without progesterone stepping in to regulate it. The eventual bleed can be prolonged and heavy, sometimes lasting more than seven days.
Structural Changes in the Uterus
When heavier periods persist over several cycles rather than being a one-time event, structural issues in the uterus become more likely culprits.
Fibroids
Uterine fibroids are noncancerous growths in the muscular wall of the uterus. They’re extremely common, affecting up to 70–80% of women by age 50, though not all fibroids cause symptoms. Fibroids that grow into the uterine cavity or distort its shape increase the surface area of the lining, which means more tissue to shed and more bleeding. They can also interfere with the uterus’s ability to contract and clamp down on blood vessels after shedding, which is the body’s natural way of slowing menstrual flow.
Adenomyosis
Adenomyosis occurs when the tissue that normally lines the uterus grows into the muscular wall itself. This causes the uterus to enlarge, sometimes to double or triple its normal size. The hallmark symptoms are heavy periods with significant clotting, along with painful cramping that may feel deeper and more diffuse than typical period pain. Adenomyosis is most common in women in their 30s and 40s and is frequently underdiagnosed because its symptoms overlap with fibroids.
Polyps
Endometrial polyps are small, usually benign growths on the uterine lining. They create extra surface area that bleeds during your period and can also cause spotting between periods. Polyps are more common after age 40 but can occur at any age.
Contraception and Medications
A copper IUD is one of the most well-known causes of heavier periods. Unlike hormonal IUDs, which typically lighten flow, a copper IUD triggers a local inflammatory response that increases bleeding. Heavier, longer periods are a common side effect, particularly in the first three to six months after insertion. For many people the flow gradually eases after that adjustment window, but some experience persistently heavier periods for as long as the device is in place.
Blood-thinning medications, including daily aspirin, can also increase menstrual flow. So can stopping hormonal birth control: if you recently came off the pill, patch, or hormonal IUD, your first several natural cycles may feel heavier simply because hormonal contraception had been thinning your lining for months or years.
Bleeding Disorders
Among women with chronically heavy periods that don’t have an obvious cause, between 5% and 24% turn out to have an underlying bleeding disorder. The most common is von Willebrand disease, a condition where the blood doesn’t clot efficiently. If your periods have been heavy since your very first one, or if you also bruise easily, bleed a long time from minor cuts, or have had excessive bleeding after dental work or surgery, a bleeding disorder is worth investigating. A simple blood test can screen for it.
Endometrial Hyperplasia
When the uterine lining grows excessively thick due to prolonged estrogen exposure without progesterone, the condition is called endometrial hyperplasia. This goes beyond just having a thick lining in one cycle. It means the cells of the lining are crowding together and, in some cases, becoming abnormal. Hyperplasia is most common in perimenopause, in women with PCOS, and in those with obesity (fat tissue produces estrogen). It matters because, left untreated, certain types can progress to uterine cancer. A heavier or longer period, or bleeding between periods, is the most common sign.
Signs Your Heavy Period Needs Evaluation
Not every heavy period requires medical attention. A single unusually heavy cycle after a stressful month or a skipped ovulation is normal. But certain patterns signal that something more is going on:
- Soaking through a pad or tampon every one to two hours for several consecutive hours
- Passing blood clots the size of a quarter or larger
- Periods lasting longer than seven days
- Needing to wake up at night to change protection
- Feeling dizzy, short of breath, or unusually fatigued, which can indicate you’re losing enough blood to become anemic
These symptoms, especially if they recur over multiple cycles, are worth bringing up with a healthcare provider. Evaluation usually starts with blood work and an ultrasound, both straightforward and noninvasive.
Iron Loss and How It Affects You
One of the most underrecognized consequences of heavy periods is iron deficiency. Every milliliter of blood you lose contains iron, and when your flow is heavy cycle after cycle, your body’s iron stores drop. Ferritin, the protein that stores iron, falls below 30 μg/L when you’re deficient, and many women with heavy periods sit well below that threshold without knowing it.
Iron deficiency doesn’t just show up as fatigue. It can cause brain fog, hair thinning, restless legs, cold hands and feet, and a frustrating inability to exercise at your usual level. If your periods have been heavier than normal for several months, checking your ferritin level (not just your standard blood count) is a practical first step. Iron stores can take months to rebuild even after the bleeding issue is addressed.
What Treatment Looks Like
Treatment depends entirely on what’s causing the heavy flow. For hormonal imbalances or anovulatory cycles, hormonal options like birth control pills or a hormonal IUD can thin the lining and dramatically reduce flow. A hormonal IUD is one of the most effective tools, often reducing bleeding by 90% or more within a few months.
For people who prefer nonhormonal options or need shorter-term help, a medication that helps blood clot more effectively at the uterine lining can reduce blood loss by about 40% per cycle. It’s taken only during the heavy days of your period.
Fibroids and polyps can often be removed through minimally invasive procedures. Adenomyosis is trickier to treat, since the abnormal tissue is embedded in the uterine wall, but hormonal management can significantly reduce symptoms. In severe cases that don’t respond to other treatments, surgical options exist.
The important thing to know is that heavy periods are not something you simply have to endure. Most causes are identifiable with basic testing, and effective treatments exist for nearly all of them.