A normal period lasts about 4 to 5 days, with most people losing only 2 to 3 tablespoons of blood total. If your period regularly stretches beyond 7 days, it’s considered prolonged, and there’s usually a specific reason behind it. The causes range from harmless hormonal shifts to structural changes in the uterus, and identifying which one applies to you is the first step toward shorter, more manageable cycles.
Hormonal Imbalances That Keep Bleeding Going
Your menstrual cycle depends on a precise back-and-forth between estrogen and progesterone. Estrogen builds up the uterine lining during the first half of your cycle, and progesterone, released after ovulation, stabilizes that lining and triggers a clean, timely shed. When ovulation doesn’t happen, progesterone never kicks in. The lining keeps thickening under estrogen’s influence, and when it finally breaks down, the bleed is heavier and longer than it should be.
This is exactly what happens with polycystic ovary syndrome (PCOS). Persistently high estrogen without adequate progesterone leads to irregular or skipped ovulation, which means the uterine lining can grow excessively thick. When it does shed, the result is prolonged, unpredictable bleeding. Over time, that sustained estrogen exposure also raises the risk of abnormal cell growth in the lining itself.
You don’t need PCOS for this to happen. Stress, significant weight changes, and even intense exercise can disrupt ovulation in any given cycle, causing the occasional period that drags on far longer than usual.
Thyroid Problems and Period Length
An underactive thyroid is one of the most overlooked causes of long, heavy periods. Thyroid hormones influence how quickly your blood clots and how your uterine lining grows. When thyroid function drops, clotting factors decrease and the lining can proliferate more than normal, both of which extend bleeding. In one study, prolonged heavy periods were the most common menstrual complaint among women with hypothyroidism, affecting over 55% of them. Elevated TSH (the marker for an underactive thyroid) was independently linked to a 2.3 times higher odds of menstrual irregularity, even after accounting for age and weight.
Thyroid issues are worth considering if your long periods come with fatigue, weight gain, or feeling cold all the time. A simple blood test can confirm or rule it out.
Structural Changes in the Uterus
Sometimes the issue isn’t hormonal at all. It’s physical. Doctors classify the structural causes of abnormal bleeding into four categories: polyps, adenomyosis, fibroids (leiomyomas), and, less commonly, malignancy or precancerous changes in the lining.
Fibroids are noncancerous growths in or around the uterine wall, and they’re extremely common. The ones most likely to cause prolonged bleeding are submucosal fibroids, which grow just beneath the inner lining of the uterus. Even a fibroid the size of a marble can cause excessive bleeding if it’s in this location, because it distorts the lining and interferes with the uterus’s ability to contract and stop the bleed efficiently.
Polyps are smaller, finger-like growths that protrude from the lining. They create extra surface area that bleeds, and they can prevent the uterus from sealing off blood vessels the way it normally would at the end of a period. Adenomyosis, where tissue that normally lines the uterus grows into the muscular wall, causes a similar effect: the uterus becomes enlarged, boggy, and less able to clamp down on bleeding.
Your IUD or Other Medications
If your periods got longer after starting a new contraceptive or medication, that’s likely not a coincidence. The copper IUD is well known for making periods heavier and longer, particularly in the first several months after insertion. Unlike hormonal IUDs, the copper version doesn’t thin the uterine lining. Instead, it creates a low-grade inflammatory response that increases blood flow during your period.
Blood thinners, some antidepressants, and certain anti-inflammatory medications can also extend bleeding by interfering with your body’s clotting ability. Hormonal contraceptives, including the pill, patch, or ring, sometimes cause prolonged spotting or breakthrough bleeding, especially when you first start them or switch formulations.
Age and Life Stage Matter
The two times in life when long periods are most common are the years right after your first period and the years leading up to menopause. Both are phases when ovulation is unreliable.
During perimenopause, which typically begins in your 40s, the ovaries start producing less estrogen and may or may not release an egg each month. This hormonal inconsistency means some cycles will be shorter, some longer, some heavier, and some barely there. A period that lasts 10 days one month and 3 days the next is a hallmark of this transition. The unpredictability can last several years before periods stop entirely.
Bleeding Disorders
About 1 in 5 women with chronically heavy periods has an underlying bleeding disorder they don’t know about. The most common is von Willebrand disease, where the blood lacks enough of a specific protein needed for clotting. If your periods have been long and heavy since they first started, and you also bruise easily, bleed a lot from minor cuts, or have had excessive bleeding after dental work or surgery, a clotting disorder is worth investigating.
When Long Periods Lead to Anemia
Losing more blood each month means losing more iron. Up to 5% of women of childbearing age develop iron-deficiency anemia specifically because of heavy periods. The symptoms creep in gradually: fatigue that sleep doesn’t fix, feeling winded climbing stairs, pale skin, dizziness, and brain fog. Many people chalk these up to being busy or not sleeping well, but if your periods are consistently long, low iron is a real possibility. A blood test measuring your iron stores can confirm it.
How Doctors Figure Out the Cause
Identifying why your period is lasting so long usually starts with blood work to check hormone levels, thyroid function, and iron status. A pelvic ultrasound is typically the first imaging step, since it can reveal fibroids, polyps, and signs of adenomyosis without any invasive procedure.
If you’re over 35 or have risk factors for abnormal cell growth, your doctor may recommend an endometrial biopsy. This involves taking a small tissue sample from the uterine lining to check for hyperplasia (overgrowth) or precancerous changes. It’s a quick in-office procedure, though it can cause cramping similar to a bad period.
Treatment Options Based on the Cause
Treatment depends entirely on what’s driving the prolonged bleeding. Hormonal options, like a hormonal IUD or oral contraceptives, work by thinning the uterine lining so there’s simply less tissue to shed. These are often the first line for hormonal imbalances and can dramatically reduce both the length and heaviness of periods.
For fibroids or polyps, removal is sometimes necessary. Small polyps and submucosal fibroids can often be taken out through a minimally invasive procedure done through the cervix, with recovery measured in days rather than weeks. Larger fibroids may require different surgical approaches depending on their size and location.
Non-hormonal medications that help blood clot more effectively can reduce bleeding by about 30 to 50% during your period and are taken only during the days you’re actively bleeding. If hypothyroidism is the culprit, treating the thyroid issue itself often brings periods back to a normal length without any additional intervention.
For people in perimenopause who aren’t bothered enough to pursue treatment, tracking your cycles and keeping an eye on iron levels may be all that’s needed until periods naturally taper off.