Endometriosis is a gynecological condition in which endometrium-like tissue is found outside the uterus on other structures throughout the pelvis, including the ovaries, fallopian tubes, bladder, pelvic floor, and in more severe cases, the bowel, diaphragm, liver, lungs, and even the brain.

According to Ken R. Sinervo, MD, the medical director of the Center for Endometriosis Care in Atlanta, “We don’t really know why endometriosis causes menstrual pain … [The pain] may have to do with where [the endometriosis] is located and how it presents.”

Untreated endometriosis can lead to adhesions, chronic inflammation, chocolate cysts (cysts filled with blood), and internal bleeding — all of which can prompt excruciating pelvic pain. Endometriosis pain isn’t limited to period pain that goes on 24/7,” says Dr. Sinvero. “Many women also experience backache and other bowel symptoms, not to be confused with IBS,” he added. 

Adenomyosis is like endometriosis, except instead of the endometrium implanting itself outside of the uterus, it is found embedded deep within the uterine muscle. In women with adenomyosis, “the uterus acts like a bruised muscle,” said Sinervo. Symptoms of adenomyosis include “painful central cramps and painful intercourse, which can hurt up until a day or two after.” Adenomyosis is usually seen in women over age 30 who have already had children. “However,” Sinervo added, “it has been seen in teenagers as well.” 

As many as three out of four women will develop uterine fibroids, but most will not experience any symptoms. Fibroids range in size from microscopic to large enough to distort the shape of the uterus.

“Uterine fibroids can turn monthly menses into a monthly nightmare by increasing not only the amount of bleeding, but the severity of period pain,” says Lauren Streicher, MD, an associate professor of obstetrics and gynecology at the Feinberg School of Medicine at Northwestern University in Chicago, and the author of Love Sex Again. “The reason behind the pain is that the uterus during the period must contract (cramp) to expel the large blood clots that often result from heavy bleeding," says Dr. Streicher. Fortunately, fibroids do not put women at increased risk of uterine cancer and very rarely become cancerous.

A copper IUD is a nonpermanent, nonhormonal form of birth control that can prevent pregnancy for up to 10 years. The device, which is placed in the uterus by a licensed healthcare provider, works by continuously releasing copper, which immobilizes sperm and prevents egg implantation.

“A copper IUD, as opposed to a progestin IUD, can make menses heavier and more painful, particularly in the first few cycles after insertion,” says Streicher. “But be aware — if you have had your copper IUD for years and suddenly develop severe period pain, look for another reason. Your IUD is unlikely to be the culprit.

Pelvic inflammatory disease is an infection of the female reproductive tract that is most commonly caused by untreated sexually transmitted infections. Left untreated, PID can cause inflammation, scarring, painful menstrual cramps, and infertility.

“[PID] most often occurs because sexually transmitted infections that cause PID can create scar tissue and adhesions in the pelvic region. During menstruation, hormones influence the uterus and surrounding structures — including the scar tissue and adhesions — which can increase inflammation, bleeding, and pain," says Shilpi Agarwal, MD, a board-certified family medicine and integrative physician in Washington, DC. If caught early, PID can be treated with antibiotics, but antibiotics won’t undo any structural damage caused by the infection. “Practice safe sex, and get tested frequently for any sexually transmitted infections, especially if you have severe period pain,” Dr. Agarwal advises.

While a female fetus is still in its mother's uterus, its own uterus develops from two structures known as Müllerian ducts. In some cases, the uterus does not form correctly, which can cause infertility, period pain, and painful intercourse. For women with structural anomalies — such as a bicornuate uterus (two uteri that lead to one cervix), septate uterus (normal uterus with a fibrous band of tissue bisecting it), unicornuate uterus (a uterus that develops from only one Müllerian duct), uterus didelphys (two uteri, two cervices, and a septum, or membrane, dividing the vaginal canal) — menstrual cramps stem from blockages and membranes dividing the uterus and vagina. 

Menstrual cramps that can’t be explained by structural defect or a reproductive condition, also known as primary dysmenorrhea, occurs at some point in almost half of all menstruating women. According to the American Congress of Obstetricians and Gynecologists, these cramps are caused by increased or imbalanced levels of prostaglandins — hormone-like fatty acids that stimulate the uterus to contract during the period. Changes in prostaglandin levels can cause more intense and frequent uterine contractions, compressing nearby blood vessels and cutting off oxygen to the uterus, thus causing painful cramps and discomfort.