Amenorrhea can occur for a variety of reasons. Some are part of the normal course of a woman's life, while others may be a side effect of medications or a sign of a medical problem.

Natural amenorrhea

During the normal course of her life, a woman may experience amenorrhea for natural reasons, such as:

  • Pregnancy
  • Breast-feeding
  • Menopause

Contraceptives

Some women who take birth control pills may not have periods. When oral contraceptives are stopped, it may take three to six months to resume regular ovulation and menstruation. Contraceptives that are injected or implanted also may cause amenorrhea, as can some types of intrauterine devices.

Medications

Certain medications can cause menstrual periods to stop, including some types of:

  • Antipsychotics
  • Cancer chemotherapy
  • Antidepressants
  • Blood pressure drugs

Lifestyle factors

  • Stress. Mental stress can temporarily alter the functioning of your hypothalamus — an area of your brain that controls the hormones that regulate your menstrual cycle. Ovulation and menstruation may stop as a result. Regular menstrual periods usually resume after your stress decreases.
  • Low body weight. Excessively low body weight interrupts many hormonal functions in your body, potentially halting ovulation. Women who have an eating disorder, such as anorexia or bulimia, often stop having periods because of these abnormal hormonal changes.
  • Excessive exercise. Women who participate in sports that require rigorous training, such as ballet, long-distance running or gymnastics, may find their menstrual cycle interrupted. Several factors combine to contribute to the loss of periods in athletes, including low body fat, stress and high energy expenditure.

Hormonal imbalance

Many types of medical problems can cause hormonal imbalance, including:

  • Polycystic ovary syndrome (PCOS). PCOS causes relatively high and sustained levels of hormones, rather than the fluctuating levels seen in the normal menstrual cycle.
  • Thyroid malfunction. An overactive (hyperthyroidism) or underactive (hypothyroidism) thyroid gland can cause menstrual irregularities, including amenorrhea.
  • Pituitary tumor. A noncancerous (benign) tumor in your pituitary gland can interfere with the hormonal regulation of menstruation.
  • Premature menopause. Menopause usually occurs between ages 45 and 55. In some women, the ovarian supply of eggs diminishes before age 40, and menstruation stops.

Structural problems

Problems with the sexual organs themselves also can cause amenorrhea. Examples include:

  • Uterine scarring. Asherman's syndrome, a condition in which scar tissue builds up in the lining of the uterus, can sometimes occur after a dilation and curettage (D&C), cesarean section or treatment for uterine fibroids. Uterine scarring prevents the normal buildup and shedding of the uterine lining.
  • Lack of reproductive organs. Sometimes problems arise during fetal development that lead to a girl being born without some major part of her reproductive system, such as her uterus, cervix or vagina. Because her reproductive system didn't develop normally, she won't have menstrual cycles.
  • Structural abnormality of the vagina. An obstruction of the vagina may prevent visible menstrual bleeding. A membrane or wall may be present in the vagina that blocks the outflow of blood from the uterus and cervix.
May. 17, 2011