Amenorrhea is typically a symptom of an underlying health issue rather than a condition itself, and it can occur for various reasons. It may naturally occur during certain life stages such as pregnancy, breastfeeding, and menopause. However, its absence can also signal problems within the ovaries, uterus, hypothalamus, or pituitary gland, or may indicate an abnormality in the genital tract. Amenorrhea is also associated with infertility, some medications, and lifestyle factors.

Amenorrhea is categorized into two types: primary and secondary.

Primary Amenorrhea (failure to menstruate by age 16)

This can be caused by several factors:

Genetic disorders: In some cases, genetic abnormalities can prevent the ovaries from functioning properly. Turner’s syndrome, where there is a missing X chromosome, can result in ovarian insufficiency and delayed or absent menstruation due to defects in genital development.
Another genetic cause is Mayer–Rokitansky–Küster–Hauser (MRKH) syndrome, where the mullerian ducts (which develop into the female reproductive system) fail to form normally, resulting in the absence of the uterus and cervix. Though individuals with MRKH have normal ovaries and secondary sexual characteristics, they experience primary amenorrhea because they lack a functioning uterus.
Issues with the hypothalamus or pituitary gland: Hormonal disruptions due to problems with these glands can lead to amenorrhea or delay the start of menstruation.
Imperforate hymen: This condition occurs when the hymen lacks an opening and fully blocks the vagina.
Transverse vaginal septum: A birth defect where a tissue wall forms across the vagina, obstructing part or all of it.
Constitutional delay of puberty: This temporary condition is characterized by a prolonged childhood phase and delayed puberty. It is not caused by a disease but reflects a variation in the normal timing of puberty. While more common in boys, girls may experience secondary sexual characteristics and menarche after age 14 and 16, respectively. Genetic or family factors may contribute to this delay, and this diagnosis is made after ruling out other causes.

Secondary Amenorrhea (absence of periods for at least six months after regular menstruation)

This type can result from various causes, including:

Natural causes: Pregnancy is the most common natural cause of secondary amenorrhea. Other physiological causes include breastfeeding and menopause.

Lactational amenorrhea is caused by high prolactin levels and low luteinizing hormone (LH), which suppress ovarian function. The duration of this condition depends on the frequency of breastfeeding.

Health conditions: Several conditions can lead to secondary amenorrhea, such as:

Pituitary tumors: Noncancerous tumors in the pituitary gland can disrupt the hormonal regulation of menstruation.
Thyroid disorders: The thyroid gland regulates metabolism and is crucial for puberty and menstruation. Both overactive and underactive thyroid function can result in menstrual irregularities, including amenorrhea.
Polycystic ovary syndrome (PCOS): A hormonal disorder common in women of reproductive age, PCOS can cause irregular periods, excess body and facial hair, ovarian cysts, and infertility. Many women with PCOS experience either amenorrhea or oligomenorrhea (irregular periods).
Hypothalamic amenorrhea: This condition occurs when the hypothalamus stops producing gonadotropin-releasing hormone (GnRH), which is essential for initiating the menstrual cycle.
Low body weight: Excessive exercise or significant weight loss can lead to Functional Hypothalamic Amenorrhea (FHA), as insufficient calorie intake disrupts normal menstrual cycles.
Hyperandrogenism: High levels of male hormones can impact the female reproductive system, caused by ovarian or adrenal tumors or certain congenital conditions.
Premature menopause: Occurring before age 40, premature menopause results from the early depletion of ovarian eggs, leading to the cessation of menstruation.

Medications and therapies: These can include:

Birth control pills: Some contraceptive pills may result in missed or absent periods. Injectables and hormonal IUDs can also cause amenorrhea. It may take a few months for a normal menstrual cycle to resume after discontinuing these methods.
Recreational drugs: Long-term use of opiates (such as heroin) has been linked to amenorrhea.
Antipsychotic drugs: These medications, used to treat conditions like schizophrenia, can lead to hormonal imbalances that result in amenorrhea.
Radiation and chemotherapy: Cancer treatments such as radiation therapy and chemotherapy can damage estrogen-producing cells in the ovaries, leading to amenorrhea.

Poor nutrition: Deficiencies in essential nutrients can affect the hypothalamus and pituitary gland, disrupting menstruation.

Stress: Stress can alter hormone levels and lead to hypothalamic amenorrhea.