The brown color of menstruation and low menstrual flow are mainly caused by the following reasons. The first one, caused by endocrine disorders. For example, polycystic ovary syndrome, hyperprolactinemia, and hyperandrogenemia may cause this condition. The second one is caused by ovarian decline. Due to the decline of ovarian function, the estrogen level decreases, resulting in darker menstruation and reduced menstrual flow. The third, due to inflammation of the endometrium, can lead to a low menstrual volume, which can become darker in color and is often accompanied by pain in the lower abdomen in clinical practice. Therefore, if your menstruation is dark in color and low in volume, you must go to the hospital for a detailed examination and then treat it according to the results.