Low menstrual flow is often caused by the following reasons: first, due to endocrine disorders, for example, due to environmental changes and stress, which can cause changes in menstruation and cause a decrease in menstrual flow. The second is due to changes in hormone levels in the body, such as increased androgens due to polycystic ovary syndrome, which can reduce menstrual flow, and increased prolactin, which can also reduce menstrual flow. Third, due to premature ovarian failure, estradiol in the body decreases, so that menstruation will also change, which often manifests clinically as low menstrual flow. Fourthly, the decrease in menstrual flow is caused by taking certain medications, such as long term use of short-acting contraceptives, which make the endometrium thinner, and this causes a decrease in menstrual flow.