A period that’s suddenly heavier than normal usually signals a temporary hormonal shift, but it can also point to structural changes in the uterus, a new medication, or an underlying condition worth investigating. Normal menstrual blood loss averages 30 to 40 mL per cycle. When that climbs above 80 mL, it crosses into what doctors consider abnormally heavy bleeding. You probably aren’t measuring in milliliters, so the practical signs matter more: soaking through a pad or tampon every hour for several consecutive hours, needing to double up on protection, passing blood clots the size of a quarter or larger, or bleeding that lasts longer than eight days.
Hormonal Imbalance Is the Most Common Cause
Your menstrual cycle depends on a careful back-and-forth between estrogen and progesterone. Estrogen thickens the uterine lining in the first half of your cycle, and progesterone stabilizes it after ovulation so it sheds in a controlled way during your period. When progesterone drops too low relative to estrogen, the lining builds up more than it should. The result is a heavier, sometimes longer bleed when it finally sheds.
This kind of imbalance can happen for all sorts of reasons: a stressful month, significant weight change, illness, travel, disrupted sleep, or a cycle where you simply didn’t ovulate. Skipping ovulation (called an anovulatory cycle) means your body never produces the progesterone surge that normally keeps the lining in check. These one-off anovulatory cycles are common and don’t necessarily signal a problem, but if they happen repeatedly, the pattern of heavy, unpredictable bleeding tends to continue.
Perimenopause and Other Life-Stage Shifts
If you’re in your late 30s or 40s, perimenopause is one of the likeliest explanations. As your ovaries begin winding down, ovulation becomes less reliable. Some months you ovulate normally, other months you don’t. During the months you skip ovulation, estrogen continues stimulating the uterine lining without progesterone stepping in to regulate it. The lining grows thicker, breaks down unevenly, and produces a heavier or more prolonged bleed. You might also notice darker blood or more clotting, which happens when older blood sits in the uterus longer before being shed.
Puberty works similarly in reverse. Teens in their first few years of menstruation often have anovulatory cycles because the hormonal feedback loop hasn’t fully matured. Heavy, irregular periods during this window are extremely common and usually settle down within a couple of years.
Fibroids, Polyps, and Structural Causes
Uterine fibroids are noncancerous growths in or on the wall of the uterus. They’re very common, especially in women over 30, and they can increase the surface area of the uterine lining or interfere with the uterus’s ability to contract and slow bleeding. The location of a fibroid matters more than its size. One that grows into the uterine cavity tends to cause heavier periods, while one on the outer surface may cause no bleeding changes at all.
Endometrial polyps, small tissue overgrowths on the uterine lining, can also trigger heavier or irregular bleeding. Both fibroids and polyps are typically identified through a pelvic ultrasound.
Adenomyosis is a less well-known cause. It happens when tissue from the uterine lining grows into the muscular wall of the uterus, causing the uterus to enlarge and making periods progressively heavier and more painful over time.
Medications and Contraception
A copper IUD is a well-documented cause of heavier periods. Unlike hormonal IUDs, the copper version contains no hormones and works by creating an inflammatory response inside the uterus. That same inflammation can make periods heavier, longer, and more painful, particularly in the first several months after insertion. For some people this improves over time, for others it persists.
Blood-thinning medications (anticoagulants and antiplatelet drugs) reduce your blood’s ability to clot, which can make menstrual bleeding noticeably heavier. If you recently started one of these medications and your periods changed, that connection is worth raising with your prescriber. Even over-the-counter anti-inflammatory painkillers taken regularly can occasionally affect clotting enough to make a difference.
Thyroid Problems and Bleeding Disorders
An underactive thyroid slows down many body processes, including the hormonal signaling that regulates your cycle. Heavy periods are sometimes one of the earliest noticeable symptoms of hypothyroidism, appearing alongside fatigue, weight gain, and feeling cold. A simple blood test can confirm or rule this out.
Bleeding disorders are an underrecognized cause of heavy periods. Von Willebrand disease, the most common inherited bleeding disorder in women, affects roughly 1 in 100 American women. Among women who have chronic heavy menstrual bleeding specifically, the prevalence jumps to between 5% and 24%. If you’ve always had heavy periods, bruise easily, bleed a lot after dental work, or have a family history of bleeding problems, an inherited clotting disorder is worth considering. Testing for it involves bloodwork that checks your clotting factors and is something you can specifically ask about.
Signs Your Heavy Period Is Causing Anemia
The most common consequence of ongoing heavy periods is iron deficiency anemia. Your body uses iron to make the hemoglobin in red blood cells, and every period depletes your iron stores. When blood loss outpaces what you can replenish through diet, you start running low.
The symptoms creep up gradually, which is why many people don’t connect them to their period. Watch for extreme tiredness that rest doesn’t fix, weakness, pale skin, frequent headaches or dizziness, shortness of breath with normal activity, cold hands and feet, brittle nails, and a sore tongue. One unusual sign: craving ice, dirt, or other non-food items. This is called pica, and it’s a surprisingly reliable signal that your iron is significantly depleted.
How to Track What’s Happening
Before you see a doctor, it helps to have specifics. Track how many pads or tampons you’re soaking through per day, whether you’re passing clots (and roughly how big they are), how many days your period lasts, and how many days fall between periods. A normal cycle repeats every 24 to 38 days with up to eight days of bleeding. Anything outside that range is useful information for your provider.
A single unusually heavy period after a stressful month, a bad illness, or a major schedule change is often a one-time hormonal blip that resolves on its own. What warrants closer attention is a pattern: periods that have been getting progressively heavier over several months, cycles that are suddenly much shorter or longer, or bleeding heavy enough that it’s interfering with daily life.
What to Expect From a Medical Workup
If your heavy bleeding persists, the initial evaluation is straightforward. Expect a pregnancy test (pregnancy complications can cause heavy bleeding even if you don’t think you’re pregnant), blood counts to check for anemia, and often a pelvic ultrasound to look for fibroids, polyps, or other structural issues. If your history suggests a thyroid problem or a bleeding disorder, additional bloodwork can check thyroid function and clotting factors.
Treatment depends entirely on the cause. Hormonal options like certain birth control methods can thin the uterine lining and significantly reduce flow. For people who prefer non-hormonal approaches, there are medications that work by preventing blood clots from breaking down too quickly, taken only during the days of your period. Fibroids or polyps that are causing problems can often be removed. And if iron deficiency anemia has developed, iron supplementation can start reversing symptoms within a few weeks, though fully replenishing your stores takes longer.