Antifertility drugs are synthetic analogs of female sex hormones (estrogen and progesterone) that prevent pregnancy by suppressing ovulation.

Norethindrone: Synthetic progesterone (progestin). Taken orally — it tricks the body into thinking it's already pregnant, preventing the release of FSH and LH hormones needed for ovulation.

Ethynylestradiol: Synthetic estrogen used in combination with norethindrone in oral contraceptive pills ("the pill"). The combination is more effective than either alone.

Mechanism: Progesterone + estrogen → negative feedback on hypothalamus → reduced GnRH → reduced FSH/LH from pituitary → no follicle maturation → no ovulation.

Other contraceptive methods involving chemistry: Mifepristone (RU-486, anti-progesterone), copper IUDs (Cu2+ ions are spermicidal), spermicidal creams (contain nonoxynol-9, a surfactant that disrupts sperm membranes).

For JEE: Norethindrone and ethynylestradiol are the two names you need to know. Both are classified as antifertility drugs under "Chemistry in Everyday Life."