Menorrhagia (or heavy menstrual bleeding) and endometriosis may often show up together, but how endometriosis affects your period flow is a more indirect process.

The inner lining of your uterus is called the endometrium. It’s made up of layers that go through a cycle of shedding and repairing every month.

When endometrium-like cells are found in locations outside of your uterus, it’s known as endometriosis. Like the endometrium, these cells can grow and bleed, causing difficulties such as scar tissue, infertility, and pain.

But, unlike the lining of the uterus, cells from endometriosis lesions have nowhere to go. They end up trapped inside your body, causing chronic inflammation.

Menorrhagia, also known as heavy menstrual bleeding (HMB) or heavy uterine bleeding, is a common experience for people living with endometriosis. Menorrhagia features unusually heavy period flow or a prolonged period lasting longer than 7 days.

Menorrhagia in endometriosis doesn’t result from blood in endometriosis lesions. Structural changes from endometriosis and chemical imbalances underlie the link between these conditions.

HMB can be a symptom of endometriosis, but endometriosis is just one of many possible causes of HMB.

Other gynecological and nongynecological conditions, such as fibroids or bleeding disorders, may also affect your menstrual period’s frequency, duration, regularity, and volume.

Menorrhagia is one presentation of abnormal uterine bleeding you may experience with endometriosis.

According to the Endometriosis Foundation of America, endometriosis regularly occurs alongside intense, painful cramping and features menorrhagia with blood clots.

Period blood clots aren’t unique to endometriosis and can be part of a regular menstrual cycle. They’re often dark or bright red blood clumps with a jelly-like appearance and consistency. Period clots the size of a quarter or larger, though, may be an indication of menorrhagia.

Other symptoms of menorrhagia can be universal, regardless of cause, and include:

  • heavy periods that soak through one or more tampons or pads per hour for several hours in a row
  • having to double-up on pads during your period
  • needing to change period wear throughout the night
  • experiencing persistent pain during your periods
  • having a period flow that limits or prevents you from doing regular activities
  • being tired, low energy, or short of breath during menstruation

Bleeding between your periods, known as intermenstrual bleeding or metrorrhagia, can also be a symptom of endometriosis. It’s another presentation of abnormal uterine bleeding and includes experiences like spotting and bleeding (sometimes heavy) between your regular periods.

Like menorrhagia, intermenstrual bleeding may have multiple causes besides endometriosis. Bleeding between your periods may also result from:

According to a review from 2022, the physiological process of menstruation is highly sensitive and complex. Even minor disruptions within any phase of the cycle could result in abnormal bleeding, such as metrorrhagia and menorrhagia. Only a healthcare professional may provide an accurate diagnosis.

Abnormal uterine bleeding patterns are just one possible symptom across a wide array of endometriosis experiences. Sometimes, endometriosis has no symptoms, and when symptoms are present, they aren’t necessarily consistent with the severity of your condition.

It’s possible to experience severe pain and discomfort with few endometriosis lesion sites, for example, or have little to no discomfort with widespread endometriosis.

Symptoms typically relate to where endometriosis is located and how its cycle of thickening and bleeding affects the structures around it.

Common symptoms of endometriosis may include:

  • chronic pelvic pain
  • intense menstrual cramping
  • deep-seated pain during or after sex
  • infertility
  • pain or discomfort when urinating or defecating
  • gastrointestinal challenges during your period, such as bloating, diarrhea, or nausea
  • fatigue

Rarely, endometriosis can travel to sites outside of the pelvic region and cause different manifestations of pain. For example, diaphragmatic endometriosis, which is where endometriosis lesions affect the diaphragm, may generate shoulder pain due to shared nerve pathways in your chest cavity.

Menorrhagia in endometriosis is indirectly caused by how endometriosis affects gynecological structures and chemical balances in your body. Treating endometriosis and managing other symptoms may help improve menorrhagia.

In all cases of menorrhagia, identifying and addressing the underlying cause is the first step toward managing heavy bleeding.

In the case of endometriosis, the condition is primarily treated through hormone therapy and surgery. Hormone therapy helps modify your hormone cycles, decreasing how often endometrial cells go through thickening and shedding.

Surgery is an option when hormone therapy isn’t effective, or if you’re experiencing fertility challenges. Surgery allows healthcare professionals to confirm the diagnosis of endometriosis and remove lesions and adhesions, which are bands of scar tissue between internal structures.

Why does endometriosis cause menorrhagia?

Endometriosis inflammation and scarring may impair the natural structures and functions of your uterus, ovaries, and fallopian tubes.

Chronic inflammation from endometriosis can also lead to an imbalance in hormones and other regulatory substances important to the menstrual cycle, resulting in abnormal bleeding like heavy, prolonged menstrual periods.

What are the symptoms of severe endometriosis?

Your symptoms and level of pain don’t necessarily indicate the severity of endometriosis. Endometriosis is staged in severity by its appearance, location, size, and the number of sites affected. Severe endometriosis is classified as “stage 4” and features extensive, deep lesions and adhesions involving multiple organs beyond your reproductive system.

It’s possible for some people to not experience severe symptoms with stage IV endometriosis, while others may experience them.

When should you see a doctor about menorrhagia?

The Centers for Disease Control and Prevention (CDC) recommends speaking with a healthcare professional about menorrhagia any time your period lasts longer than 7 days or requires you to change your tampon or pad hourly.

Menorrhagia (heavy menstrual bleeding) and endometriosis are often co-occurring. You may experience menorrhagia without endometriosis, and endometriosis doesn’t always cause abnormal bleeding symptoms like menorrhagia.

Endometriosis may indirectly cause menorrhagia by affecting the structures of your reproductive system and altering chemical balances necessary for regulating your menstrual cycle.

Hormone therapy and surgery can treat endometriosis and may help improve symptoms such as HMB, prolonged periods, and bleeding between periods.