OCP – Oral Contraceptive Pills

Oral contraceptive pills (OCPs)

• OCPs are one of the most common and effective methods of birth control.
• They primarily rely on synthetic versions of the female ovarian hormones—estrogen and progesterone (progestin)—to alter the body’s natural reproductive cycle.
• Depending on their composition, they are broadly classified into two categories:
  • Combination Pills (containing both estrogen and progestin) and
  • Progestin-Only Pills (POPs).

1. Combination Oral Contraceptive Pills

These contain a mixture of synthetic estrogen (usually ethinyl estradiol) and a progestin. They work via a highly effective triple mechanism of action:

A. Inhibition of Ovulation (Primary Mechanism)

The steady, daily dose of synthetic estrogen and progestin exerts a negative feedback effect on hypothalamus and anterior pituitary, suppressing the secretion of FSH and LH. Consequently, ovulation is completely prevented; without the release of an oocyte, fertilization cannot occur.

B. Alteration of Cervical Mucus

Progestin thickens the cervical mucus, making it dense and viscous to create a physical barrier. This renders the cervix hostile to sperm; the altered environment actively blocks, traps, and destroys sperm cells before they can enter the uterus.

C. Alteration of the Endometrium

The hormonal combination alters the normal proliferation and secretory phases of the uterine lining – endometrium, which becomes thin, atrophic, and poorly vascularized, preventing implantation of the blastocyst, even if fertilization occurs.

2. Progestin-Only Pills (POPs or “Mini-Pills”)

As the name suggests, these contain no estrogen. They are often prescribed for individuals who are breastfeeding or cannot tolerate estrogen due to medical reasons (e.g., cardiovascular risks).

Mode of Action:

• Primary Effect: Their primary mechanism relies heavily on thickening the cervical mucus and thinning the endometrium, just like the combination pill
• Secondary Effect:  makes the uterine environment hostile to sperm and implantation.

**Non-Steroidal Alternatives:

While standard OCPs are hormonal, there are also unique non-steroidal formulations like Centchroman or Ormeloxifene, famously developed in India as “Saheli” – once a week pill. Instead of altering hormone levels or stopping ovulation, it acts as a Selective Estrogen Receptor Modulator (SERM). It speeds up the transport of the fertilized ovum through the fallopian tubes while simultaneously preventing the endometrium from preparing for implantation, acting purely as an anti-implantation agent.