Adenomyosis happens when the uterine lining (endometrium) grows into the muscle layer (myometrium). It’s often compared to endometriosis because both involve endometrial tissue, but they differ in location: endometriosis involves tissue outside the uterus, while adenomyosis is inside the uterine wall. The misplaced tissue responds to hormonal cycles—thickening and breaking down each month—causing inflammation and pain because the tissue can’t exit the muscle layer.

Who gets it Adenomyosis can affect anyone who menstruates but is most common between ages 40–50 and in people who’ve given birth. Estimates vary, but roughly 1 in 10 people may have it. It often coexists with other conditions, like fibroids and sometimes endometriosis.

Symptoms Many people (about one-third) have no symptoms, but when present the most common problems are:

• Heavy, painful periods
• Irregular bleeding
• Premenstrual pelvic pain
• Pain during sex
• Painful urination or bowel movements
  Heavy bleeding raises the risk of iron deficiency and anemia, which can cause fatigue and dizziness. Adenomyosis has been found in some people with fertility issues, though clear evidence that it reduces fertility is limited.

Cause The exact cause is unknown. It’s considered hormone-dependent—symptoms usually ease after menopause—while genetics, immune factors, and prior uterine surgery (including C-section) may play roles. The condition frequently appears alongside fibroids and, less often, endometriosis.

Diagnosis Diagnosis can be tricky because symptoms overlap with many other conditions (endometriosis, IBS, pelvic inflammatory disease, perimenopause). There’s no universal diagnostic standard. Transvaginal ultrasound detects many cases; if unclear, an MRI may be used.

Treatment There’s no single cure that targets the root cause, so treatment focuses on relieving symptoms:

• Conservative: NSAIDs for pain, iron supplements for anemia
• Hormonal: Progestin-only pills, hormonal IUDs (IUS), combined hormonal contraceptives to thin the lining and reduce bleeding
• Non-surgical procedure: Uterine artery embolization (UAE) can shrink affected tissue but isn’t permanent and may not be suitable if you want to conceive
• Surgery: Hysterectomy is the definitive option if other treatments fail and future pregnancy is not desired

Quick summary

• Adenomyosis: endometrial tissue growing into the uterine muscle.
• Affects about 1 in 10 people, most commonly ages 40–50.
• Often confused with endometriosis; symptoms include heavy, painful periods and pelvic pain.
• Cause is unclear; diagnosis can require ultrasound or MRI.
• Treatments range from pain relief and hormonal options to procedures or hysterectomy for severe cases.