Oral Contraceptives (Birth Control Pills)

• Oral contraceptives are drugs used to prevent pregnancy and typically contain synthetic estrogen and progesterone.

Normal Mechanism of Estrogen and Progesterone in Pregnancy

• Egg Production & Fertilization: The ovaries produce an egg (ovum) and release it into the fallopian tube, where it may be fertilized by sperm.
• Uterus Preparation: The uterus prepares for a fertilized egg by thickening the endometrium (uterine lining).

• Role of Hormones:

• 1. Estrogen thickens the endometrium.
  2. Progesterone thickens both the endometrium and the cervical mucus, preventing sperm from passing.

• Menstruation: If fertilization doesn’t occur, levels of progesterone and estrogen decline, leading to menstruation.

Types of Oral Contraceptives

1. Combined Pills (Estrogen + Progesterone)

   • Mechanism:
     • Estrogen prevents FSH secretion (via negative feedback), suppressing ovulation.
     • Progesterone prevents LH release, further preventing ovulation and thickening the cervix.
     • Both hormones alter the endometrium to prevent implantation.
   • Effectiveness: Highly effective.
   • Side Effects: Weight gain, nausea, vomiting.

2. Progesterone-Only Pills (Mini Pills)

   • Mechanism:
     • Progesterone prevents LH release, inhibiting ovulation.
     • Thickens cervical mucus to prevent sperm entry.
   • Effectiveness: Less effective than combined pills, suitable for women who can’t use estrogen.

Summary of Oral Contraceptives

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