Several things can make your period heavier than usual, ranging from normal hormonal shifts to underlying medical conditions. A typical period produces about 30 to 40 ml of blood over three to seven days. Bleeding is considered heavy when it exceeds 80 ml per cycle or lasts longer than seven days, and passing blood clots is an independent predictor of heavier-than-normal flow. Understanding what drives that extra bleeding can help you figure out whether what you’re experiencing is a temporary fluctuation or something worth investigating.
Hormonal Imbalance Between Estrogen and Progesterone
The most common reason for heavier periods is a shift in the balance between your two main reproductive hormones. Estrogen builds up the lining of your uterus each cycle, and progesterone keeps that buildup in check. When these two work together properly, the lining stays a normal thickness and sheds predictably. But when progesterone levels drop too low relative to estrogen, sometimes called estrogen dominance, estrogen essentially works overtime. The uterine lining grows thicker than it should, and when it finally sheds, there’s simply more tissue and blood to come out.
This imbalance can happen during perfectly normal life stages. Perimenopause is one of the most common times for it, because ovulation becomes irregular and progesterone production drops. Teenagers in their first few years of menstruating often experience the same thing, since their cycles haven’t settled into a regular ovulatory pattern yet. Stress, significant weight changes, and polycystic ovary syndrome can all disrupt ovulation in a similar way, leaving estrogen unopposed for longer stretches of each cycle.
Fibroids, Polyps, and Other Structural Causes
Growths in or on the uterus are a major cause of heavier bleeding, particularly for people in their 30s and 40s. Uterine fibroids are dense, noncancerous muscle tumors that can increase menstrual flow through several mechanisms at once. They enlarge the inner surface area of the uterus, meaning there’s more lining to shed. They also interfere with the uterus’s ability to contract and clamp down on blood vessels after shedding, which is the body’s main way of stopping menstrual bleeding. Fibroids can compress surrounding veins, creating enlarged pools of blood within the uterine wall that contribute to heavier flow.
Endometrial polyps, which are softer finger-like growths on the uterine lining, cause similar problems on a smaller scale. They add extra vascularized tissue that bleeds during your period. Both fibroids and polyps can be detected with an ultrasound, and their location matters as much as their size. A small fibroid pressing into the uterine cavity often causes more bleeding than a larger one growing on the outer surface.
Adenomyosis
Adenomyosis happens when the tissue that normally lines the uterus starts growing into the muscular wall itself. This triggers a cascade of problems: the embedded tissue creates new blood vessels in the muscle (a process called neoangiogenesis), disrupts the uterus’s normal contractions, and causes chronic inflammation. All of these increase menstrual blood loss. The abnormal blood vessel growth is particularly significant because it brings more blood supply directly into the areas that bleed during your period.
Adenomyosis also tends to cause intense cramping because the uterine muscle contracts harder and more erratically than normal. If your periods have gotten progressively heavier and more painful over time, especially in your late 30s or 40s, adenomyosis is one of the more likely explanations.
Prostaglandins and Your Body’s Clotting Response
Your uterus produces chemical messengers called prostaglandins that control how blood vessels in the uterine lining open and close. In people with heavier periods, the balance of these messengers tilts toward vasodilation, meaning the blood vessels stay wider and bleed more freely. Specifically, the uterine tissue produces more of the types that relax blood vessels and prevent clotting, while producing relatively less of the type that constricts vessels and slows bleeding.
This is one reason why anti-inflammatory painkillers like ibuprofen can reduce menstrual flow by 20 to 30 percent. They work by blocking prostaglandin production across the board, which shifts the balance back toward less bleeding. Taking them at the start of your period, before heavy flow begins, tends to be more effective than waiting.
Bleeding Disorders
Between 5 and 20 percent of people investigated for heavy periods turn out to have von Willebrand disease, a condition where the blood doesn’t clot properly. It’s the most common inherited bleeding disorder, and heavy periods are often the first and most obvious symptom. Other clotting disorders, including platelet function problems, can have a similar effect.
Clues that a bleeding disorder might be involved include heavy periods that started from your very first cycle (rather than developing later in life), a tendency to bruise easily, prolonged bleeding after dental work or minor cuts, and a family history of bleeding problems. These conditions are underdiagnosed partly because heavy periods get normalized, but they’re identifiable with blood tests.
Thyroid Problems
An underactive thyroid can make periods heavier through an indirect route. Low thyroid hormone disrupts ovulation, which creates the same kind of estrogen-progesterone imbalance described above. It can also increase production of prolactin, a hormone normally associated with breastfeeding, which further suppresses ovulation. The result is a thicker uterine lining and heavier shedding. Thyroid issues are straightforward to test for with a simple blood draw, and treating the thyroid problem typically brings periods back to normal.
Copper IUDs
If you have a copper IUD and your periods got noticeably heavier after insertion, that’s a well-documented side effect. In clinical studies, menstrual blood loss increased from an average of about 37 ml before insertion to roughly 54 to 61 ml in the first two periods afterward. That’s an increase of roughly 50 percent. The heavier bleeding tends to be most noticeable in the first two cycles and often decreases somewhat by the third, though periods generally remain heavier than they were before the IUD for as long as it stays in place.
Hormonal IUDs, by contrast, typically have the opposite effect and are sometimes used specifically to treat heavy periods.
Blood Thinners and Other Medications
Blood-thinning medications are one of the most significant drug-related causes of heavier periods. Around 70 percent of menstruating people on oral anticoagulants experience heavier bleeding. The effect varies by medication: some carry more than double the risk of heavy menstrual bleeding compared to others. If you’ve started any blood-thinning medication and noticed a change in your flow, your prescribing provider may be able to adjust the type of anticoagulant.
Aspirin, even at low daily doses, can also increase menstrual volume because it impairs platelet function. Some antidepressants in the SSRI class have a mild blood-thinning effect that occasionally shows up as heavier periods.
Other Factors That Can Increase Flow
A few additional variables are worth noting. Endometriosis, where uterine-like tissue grows outside the uterus, is listed alongside fibroids and adenomyosis as a recognized cause of heavier bleeding. Significant weight gain can increase estrogen levels because fat tissue produces its own estrogen, compounding any existing hormonal imbalance. Approaching menopause is one of the most common reasons periods get heavier, as cycles become increasingly anovulatory in the years before they stop entirely.
Periods can also temporarily run heavier after a miscarriage or pregnancy, during high-stress periods, or when stopping hormonal birth control that had been suppressing flow. In most of these cases, the change is self-limiting and resolves within a few cycles. When heavier bleeding persists for three or more cycles, or when it’s heavy enough that you’re soaking through a pad or tampon every hour for several consecutive hours, that pattern is worth getting evaluated with bloodwork and imaging to identify the specific cause.