Causes

Amenorrhea can occur for a variety of reasons. Some are normal, while others may be a side effect of medication or a sign of a medical problem.

Natural amenorrhea

During the normal course of your life, you may experience amenorrhea for natural reasons, such as:

• Pregnancy
• Breastfeeding
• Menopause

Contraceptives

Some people who take birth control pills (oral contraceptives) may not have periods. Even after stopping birth control pills, it may take some time before regular ovulation and menstruation return. 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
• Allergy medications

Lifestyle factors

Sometimes lifestyle factors contribute to amenorrhea, for instance:

• Low body weight. Excessively low body weight — about 10% under normal weight — interrupts many hormonal functions in the 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 activities that require rigorous training, such as ballet, may find their menstrual cycles interrupted. Several factors combine to contribute to the loss of periods in athletes, including low body fat, stress and high energy expenditure.
• 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.

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 thyroid gland (hyperthyroidism) or underactive thyroid gland (hypothyroidism) 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 begins around age 50. But, for 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 missing parts of the reproductive system, such as the uterus, cervix or vagina. Because the reproductive system didn't develop fully, menstrual cycles aren't possible later in life.
• 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.