This is an excerpt about endometriosis adapted from Doing Harm: The Truth About How Bad Medicine and Lazy Science Leave Women Dismissed, Misdiagnosed, and Sick by Maya Dusenbery.

Ellen got her period at age eleven, and, after a few years, the mild cramps she’d experienced at first began to morph into a different beast entirely. “The pain was shifting from my uterus to my hips, and it got worse and worse and worse. And it was a different kind of pain than I was used to. It felt like a burning, inflammatory pain, like if you had a hot coffee mug and pushed it against your joints.” Her back was painful and stiff, all the way up to her neck. “The result was that a lot of times I couldn’t really walk or stand or sit. I could basically only move back and forth in bed every so often to distribute the pain around.”

In high school, she started missing school, usually the one or two days right before her period began, which is when the pain peaked, and became a regular visitor at the nurse’s office. “I think they kind of thought that I was making it up a little bit. Because they were like, ‘Oh yeah, it’s you again.’ At least once a month, I’d have to be taken home from school by my mom and carried into the house.” A couple times she ended up in the hospital. “They didn’t really know what to do. They just kind of gave me morphine, and the next morning they sent me home.”

Perhaps no disease has been more hampered by the normalization of women’s pain as endometriosis. A common, poorly understood disease that affects at least 6.3 million women and other people with a uterus in the United States, endometriosis occurs when a substance similar to the endometrium (the tissue that lines the uterus in preparation for implantation of a fertilized egg and, if that fails to happen, bleeds and sheds during menstruation) is found in other parts of the abdominal cavity. This tissue responds to the hormones that trigger menstruation, also bleeding and attempting to shed each month. The result is pain, inflammation, and the formation of nodules, cysts, and scar tissue.

The disease’s symptoms include pain before and during periods, fatigue, heavy bleeding, painful bowel movements, painful urination, and diarrhea and constipation during menstruation. About a third of patients with endometriosis are infertile, and more than half experience pain during sex. Some endometriosis patients have pain all the time, not just around their period; the condition is thought to explain up to 90% of cases of chronic pelvic pain in women.

To get officially diagnosed, you have to undergo a surgical procedure that identifies the endometriosis lesions. Which means that you have to convince your doctor that your symptoms are not just “killer cramps,” a task that proves all but impossible for many women. In the United States, on average, it takes ten to twelve years between the time the symptoms begin — which, for 60% of patients, is before age twenty —and getting a diagnosis. According to the Endometriosis Association’s research registry, 61% of endometriosis patients had been told by health care providers that nothing was wrong with them.

The widespread belief — shared by the medical system and the public alike — that menstrual pain is “normal” poses a barrier to the prompt diagnosis of endometriosis even before a patient steps foot in a doctor’s office. A 2006 study of women eventually diagnosed with the disease found that one of the reasons for the diagnostic delay was that the women themselves didn’t see a reason to ask a doctor about their painful periods. They figured they were just one of those “unlucky” people who got bad cramps. And really, how would they know that their periods weren’t normal? There’s so much stigma around menstruation that many young women are left without any point of comparison.