Contraceptives

Contraceptive Use in the United States

  • Approximately 62% of women of reproductive age (ages 15–44) use some form of contraceptive method. This indicates that a significant portion of women actively seeks to control their reproductive health through various means.

  • Of these women, 64% utilize reversible methods, such as hormonal methods, intrauterine devices (IUDs), or condoms. Reversible methods allow women to stop using them whenever they choose and regain their fertility quickly.

  • The remaining women primarily rely on surgical options like female or male sterilization, which are permanent methods of contraception.

  • The pill and female sterilization have been the leading contraceptive methods in the U.S. since 1982, showing the enduring popularity and reliability of these options among women.

  • With perfect use, the pregnancy rate with oral contraceptives is less than 1%, meaning even fewer women would become pregnant if they take the pill exactly as prescribed. However, the typical use failure rate is higher because real-life scenarios often involve missing doses or taking them at inconsistent times.

Mechanism of Action of Oral Contraceptives

  • Hypothalamic-Pituitary-Gonadal Axis: This is the body's hormonal system that controls reproduction. It involves multiple glands and hormones that signal one another and ensure proper reproductive function.

    • The hypothalamus, a small region of the brain, releases a hormone called gonadotropin-releasing hormone (GnRH). This hormone is crucial as it tells the pituitary gland to release other key hormones.

    • In response, the pituitary gland releases:

      • Luteinizing hormone (LH): This hormone triggers ovulation and supports various processes in reproduction.

      • Follicle-stimulating hormone (FSH): This hormone aids in the growth and maturation of eggs in the ovaries.

    • LH and FSH stimulate the ovaries to produce important hormones: estrogen and progesterone. These hormones, in turn, provide feedback to inhibit the release of more GnRH, LH, and FSH, creating a balanced hormonal environment.

  • Oral Contraceptive Mechanism: The primary function of the pill is to prevent ovulation, the process during which an ovary releases an egg.

    • Estrogen and/or progesterone are administered in low doses through these pills. Their introduction into the body inhibits the release of LH and FSH from the pituitary gland, effectively stopping ovulation from occurring.

    • Without ovulation, there’s no egg available for sperm to fertilize, significantly reducing the chances of pregnancy.

Detailed Site of Action

  • Estrogen: This hormone inhibits the release of FSH from the pituitary gland, which blocks the maturation of follicles (structures in the ovaries that contain eggs).

  • Progesterone: This hormone inhibits LH release and also plays a role in altering how the fallopian tubes move eggs and affects the motility of sperm (how effectively they can swim to reach an egg).

  • Uterine Endometrium:

    • Estrogen leads to rapid proliferation, meaning it encourages the thickness of the uterine lining (endometrium), which is important for pregnancy.

    • Progesterone, however, creates a thicker, more vascular (blood-rich) tissue that is prepared for a potential pregnancy. Together, they result in a thinner endometrium, which is unfavorable for blastocyst implantation (the stage of development when an embryo attaches to the uterine lining).

Types of Oral Contraceptives
Three Types of Steroidal Contraceptives

  1. Combined Contraceptives (Estrogen and Progesterone)

    • There are different formulations based on the dosage schedule:

      • Monophasic: Provides the same dosage of hormones for 21 days, followed by a week of placebo pills which allow for a withdrawal bleed similar to a period.

      • Biphasic: Maintains constant estrogen levels while increasing progesterone doses at a predetermined point, then a week of placebo.

      • Triphasic: Adjusts both estrogen and progesterone levels through three different phases, followed by a week of placebo pills.

      • Quadraphasic: While this is less common and involves four different hormone levels, it can create a more complex pill-taking schedule.

    • Main Estrogen Component: Most combined pills use ethinyl estradiol, a synthetic version of a natural hormone called 17-beta estradiol. This compound is designed to have improved absorption in the body due to its modified structure, which reduces the first-pass effect in the liver.

    • Progestins: Other types of hormones, like Norgestrel and Norethindrone, are used in the formulation of these pills, which have minimal estrogenic activity and can sometimes have anti-androgenic effects, potentially causing side effects like acne. Some forms, like Drospirenone, also help in preventing water retention by having an anti-mineralocorticoid effect.

  2. Progestin-Only Contraceptives (Mini Pills)

    • These are specifically designed for women who cannot use estrogen—this includes breastfeeding mothers, smokers over 35, and women with certain health risks.

    • The mechanism of action involves:

      • Inhibiting ovulation (though not always reliably),

      • Thickening cervical mucus, making it more difficult for sperm to reach an egg,

      • Thinning the uterine lining, making it harder for an embryo to implant if ovulation does occur.

    • Risks include potential bone density loss, mood changes like depression, weight gain, and irregular bleeding, which can cause some discomfort and concern.

  3. Intrauterine Devices (IUDs)

    • These are not pills but small devices inserted into the uterus. They release small amounts of progesterone (like Mirena, effective for 5 years, or Skyla, effective for 3 years) to prevent pregnancy.

    • They work by thickening cervical mucus, altering the uterine environment, and sometimes inhibiting ovulation.

Contraceptive Methods and Their Administration

  • Combined Contraceptives:

    • Most of these are taken in a pill form, with a 3-week active pill schedule followed by a 1-week placebo, thus allowing for a menstrual-like withdrawal bleed. Some women choose extended packs, which may allow for using the pill for three months continuously, resulting in fewer periods (as little as four periods per year).

    • Other delivery methods include:

      • Patch: A transdermal patch that releases hormone into the body, placed on the skin and changed weekly for three weeks.

      • Ring: A flexible ring placed inside the vagina, releasing hormones and changed monthly.

Benefits of Combination Estrogen and Progesterone Contraceptives

  • These contraceptives help decrease medical issues like menstrual pain and heavy bleeding, leading to improved quality of life. They also have protective effects against various health conditions, reducing the risks of ovarian cancer, uterine cancer, endometriosis, and conditions like fibrocystic breast disease.

Side Effects of Oral Contraceptives
Estrogen Side Effects

  • Some women might experience nausea, weight gain, increased blood pressure, and a heightened risk of thromboembolic events (such as blood clots, strokes).

Progestin Side Effects

  • Common side effects include acne, weight gain, tenderness in the breasts, fatigue, and negative effects on cholesterol levels (both LDL and HDL), which could contribute to hypertension.

Absolute Contraindications for Combination Contraceptives

  • Certain conditions mean women shouldn’t use them at all:

    • Current pregnancy,

    • Unexplained vaginal bleeding,

    • Severe liver disease or history of liver tumors,

    • History of thromboembolic events or ischemic heart disease,

    • Women age 35 or older who smoke heavily.

Relative Contraindications (Require Monitoring)

  • Some health issues might make using these contraceptives riskier, so close monitoring is advisable:

    • Hypertension (high blood pressure),

    • High cholesterol (hyperlipidemia),

    • Chronic headaches (especially migraines),

    • Uterine fibroids, which could complicate menstruation,

    • Depression and existing gallbladder disease,

    • Renal issues (kidney disease).

Progestin-Only Contraceptives

  • These are especially designed for those who cannot take estrogen; they include options like:

    • Mini Pills: Taken daily without breaks (although breakthrough bleeding can be common).

    • Injection: Administered intramuscularly, providing three-month protection (e.g., Medroxyprogesterone acetate).

    • IUDs (e.g., Mirena, Skyla),

    • Implants (e.g., Nexplanon, providing long-term birth control stored in the skin).

Emergency Contraception

  • Emergency contraception consists of high-dose progesterone taken shortly after unprotected intercourse and is most effective within 72 hours but may work up to 120 hours later in some cases.

  • Common dosage: Levonorgestrel given as 0.75 mg taken 12 hours apart or a single dose of 1.5 mg.

  • Effectiveness ranges from 75% to 89% if taken within 72 hours, with up to 95% effectiveness if taken within a day.

  • Side effects may include some nausea but are generally less severe compared to concerns with combined methods.

  • A notable product available is Plan B, which serves as a well-known emergency option.

Drug Interactions with Oral Contraceptives

  • Some medications may lessen the effectiveness of oral contraceptives. These include:

    • Anticonvulsants, such as barbiturates, phenytoin, and carbamazepine, which are used for epilepsy and other conditions,

    • Certain antibiotics like rifampicin, amoxicillin, and ampicillin may interact negatively,

    • St. John’s wort, a supplement some take for mood, can have a similar effect.

    • Therefore, it’s vital for women on these medications to use backup contraceptive methods to ensure continued protection against unintended pregnancy.

Special Considerations for Drospirenone

  • Drospirenone is a unique progestin with anti-mineralocorticoid activity, which may raise blood potassium levels slightly, requiring monitoring in some cases.

  • Caution should be exercised when taken with other medications that also affect potassium levels such as NSAIDs, ACE inhibitors.

  • Although rare, the use of Drospirenone has been associated with increased blood clot risks, potentially linked to its estrogen-like effects.

Summary

  • This overview discusses different types of oral contraceptives, including combined and progestin-only options, along with emergency contraception. It highlights important notes on side effects, contraindications, and interactions with other medications which may influence the effectiveness of these contraceptives.