How do oral contraceptives (OCs) cause amenorrhea?

From the Guidelines

Oral contraceptives (OCs) typically cause amenorrhea by suppressing ovulation and altering the hormonal balance, leading to a decrease in menstrual bleeding 1.

Mechanism of Action

• The hormonal components of OCs, such as estrogen and progesterone, regulate the menstrual cycle by inhibiting the release of gonadotropin-releasing hormone (GnRH), which in turn suppresses the release of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) 1.
• This suppression of LH and FSH prevents ovulation and thins the endometrial lining, reducing the likelihood of menstrual bleeding 1.

Clinical Considerations

• If a woman experiences amenorrhea while using OCs, it is essential to rule out pregnancy if clinically indicated 1.
• In some cases, alternative contraceptive methods may be considered if the woman finds the amenorrhea unacceptable 1.
• Reassurance that amenorrhea is generally not harmful can help reduce discontinuation of OCs 1.

From the FDA Drug Label

Although the primary mechanism of this action is inhibition of ovulation, other alterations include changes in the cervical mucus (which increase the difficulty of sperm entry into the uterus) and the endometrium (which reduce the likelihood of implantation)

Oral contraceptives (OCs) cause amenorrhea by inhibiting ovulation and altering the endometrium, which reduces the likelihood of implantation. This is the primary mechanism by which OCs prevent pregnancy and lead to amenorrhea. 2

From the Research

Mechanism of Amenorrhea Induction by Oral Contraceptives

• Oral contraceptives (OCs) can induce amenorrhea in many women by suppressing the hypothalamic-pituitary-ovarian axis, leading to a decrease in estrogen and progesterone levels 3, 4.
• Continuous use of OCs, without the hormone-free interval, can relieve menstrual-cycle-related symptoms and induce amenorrhea in 80% to 100% of women by 10 to 12 months of use 3.
• The traditional method of taking OCs continuously can produce weight gain and other side-effects, but is a cheap option for inducing amenorrhea 4.

Hormonal Changes Associated with OC-Induced Amenorrhea

• Studies have shown that women with OC-induced amenorrhea have low normal levels of urinary estrogen excretion and plasma LH and FSH values 5.
• Prolactin levels can be elevated in some women with OC-induced amenorrhea, particularly those with galactorrhea 5.
• The pituitary response to synthetic LH-RH is similar to that found in the early follicular phase of the ovulatory cycle, indicating that the pituitary is capable of synthesizing and secreting LH and FSH 5.

Comparison with Other Methods of Inducing Amenorrhea

• Other methods of inducing amenorrhea, such as using Gonadotrophin Releasing Hormone (GnRH) analogues or synthetic steroids, can be effective but may have more side-effects and are often more expensive than OCs 4.
• The use of OCs to induce amenorrhea is a safe and effective method, with many women opting for extended-cycle or continuous regimens 3.