What is the reason for not having a period?

Patient's question:

Female, 20 years old, previously normal

Doctor's answer:

There are two major categories of factors affecting menstruation:
1. Disorders of neuroendocrine function: Such as excessive mental stress, changes in environment and climate, malnutrition or metabolic disorders, and influences from gynecological inflammatory diseases. The primary issue lies in defects in the hypothalamic-pituitary-ovarian axis, which is essentially menstrual disorders.
2. Organic lesions or drug-related causes: Including local inflammation, tumors, and developmental abnormalities of the reproductive organs, as well as malnutrition.