Menstrual irregularities can have a variety of causes, including pregnancy, hormonal imbalances, infections, diseases, trauma, and certain medications.

Causes of irregular periods (generally light) include:

  • Perimenopause (generally in the late 40s and early 50s)
  • Primary ovarian insufficiency (POI)
  • Eating disorders (anorexia nervosa or bulimia)
  • Excessive exercise
  • Thyroid dysfunction (too much or too little thyroid hormone)
  • Elevated levels of the hormone prolactin, which is made by the pituitary gland to help the body produce milk
  • Uncontrolled diabetes
  • Cushing's syndrome (elevated levels of the hormone cortisol, used in the body's response to stress)
  • Late-onset congenital adrenal hyperplasia(problem with the adrenal gland)
  • Hormonal birth control (birth control pills, injections, or implants)
  • Hormone-containing intrauterine devices (IUDs)
  • Scarring within the uterine cavity (Asherman's syndrome)
  • Medications, such as those to treat epilepsy or mental health problems

Common causes of heavy or prolonged menstrual bleeding include:

  • Adolescence (during which cycles may not be associated with ovulation)
  • Polycystic ovary syndrome (PCOS) (bleeding irregular but heavy)
  • Uterine fibroids (benign growths of uterine muscle)
  • Endometrial polyps (benign overgrowth of the lining of the uterus)
  • Adenomyosis (the presence of uterine lining in the wall of the uterus)
  • Nonhormonal IUDs
  • Bleeding disorders, such as leukemia, platelet disorders, clotting factor deficiencies, or (less common) von Willebrand disease
  • Pregnancy complications (miscarriage)

Common causes of dysmenorrhea (menstrual pain) include:

  • Endometriosis (uterine lining grows outside the uterus)
  • Uterine abnormalities (fibroids or adenomyosis)
  • IUDs
  • Pelvic scarring due to sexually transmitted infections, such as chlamydia or gonorrhea
  • Heavy menstrual flow