Black and clotted menstrual blood can be concerning. The color often indicates older blood that has taken longer to exit the uterus, oxidizing and darkening in the process. Clots are generally normal, especially during heavier flow, but large or excessive clotting could signal an underlying issue. While usually harmless, it's essential to consult a doctor if you experience significant pain, heavy bleeding, or other unusual symptoms, as it could indicate hormonal imbalances, fibroids, or other conditions.