Which compound is used in contraceptive pills?

Question

UnlockIAS · Accepted Answer

Correct — B, Levonorgestrel. It is a progestin — a laboratory-made analogue of the natural hormone progesterone — and it is the workhorse molecule of hormonal contraception worldwide. It was patented in 1960, introduced for medical use in 1970 in combination with the oestrogen ethinylestradiol, and it sits on the World Health Organization's Model List of Essential Medicines. It reaches contraceptive pills in three distinct ways, and the doses are worth keeping apart. In a combined oral contraceptive it is taken daily alongside ethinylestradiol, in monophasic strengths of 100–250 micrograms or triphasic strengths of 50, 75 and 125 micrograms. In a progestogen-only pill, the so-called mini-pill, it is used alone at roughly 30 micrograms a day. As an emergency contraceptive — the morning-after pill, sold over the counter in India — it is a single 1.5 mg dose, or two 0.75 mg doses twelve hours apart, taken within 72 hours of unprotected sex, with the effect falling the longer one waits. The same molecule is the active agent in hormonal intrauterine devices such as Mirena and in implants such as Jadelle. Its mechanism is straightforward: it prevents or delays ovulation, so no egg is released, and it thickens cervical mucus so that sperm cannot get through. The International Federation of Gynecology and Obstetrics states that the progestogen-only emergency pill works by inhibiting ovulation and thickening cervical mucus, that it is ineffective once ovulation has already occurred, and that it has not been found to act on implantation — which is why it is classed as a contraceptive and not as an abortifacient. The other three options are all real, widely used medicines, but each belongs to an unrelated therapeutic class.

Why the other options are wrong — (a) Cholecalciferol is vitamin D₃ — the form the skin manufactures from a cholesterol derivative under ultraviolet-B light and the form sold as a supplement. Its function is to raise the absorption of calcium and phosphate from the gut; deficiency produces rickets in children and osteomalacia in adults. It is chemically a secosteroid, a broken-ring relative of the steroids, and that faint family resemblance to the steroid sex hormones is the only thing that makes it look plausible here. It is a nutrient, not a drug that acts on ovulation.  (c) This is the booklet's spelling of venlafaxine, a serotonin–noradrenaline reuptake inhibitor prescribed for major depressive disorder and for anxiety disorders. It raises the amount of serotonin and noradrenaline available at the synapse, so it acts on the brain and not on the reproductive axis, and it has no contraceptive property at all. Its only pull is that it sounds convincingly pharmaceutical to a candidate who recognises none of the four names.  (d) The booklet's spelling of cetirizine, a second-generation H1 antihistamine taken for allergic rhinitis, hay fever and urticaria. It blocks the histamine H1 receptor and is called non-sedating because, unlike the older antihistamines, it crosses the blood–brain barrier poorly. It is among the most familiar over-the-counter medicines in India, and that familiarity — not any relevance to reproduction — is exactly what makes it a tempting tick for a candidate guessing on name recognition.

Concept: Hormonal contraception works by imitating the body's own signal that ovulation is unnecessary. The menstrual cycle runs on a feedback loop: the hypothalamus releases GnRH in pulses, the anterior pituitary answers with FSH and LH, the ovary responds by maturing a follicle and secreting oestrogen and progesterone, and a surge of LH triggers ovulation. Supply a steady level of progestogen from outside — with or without an oestrogen — and the pulsing is damped, the LH surge does not occur, and no egg is released. Progestogens add two further barriers: they thicken cervical mucus so sperm cannot ascend, and they thin the endometrium. Vocabulary matters here, because examiners exploit it. Progesterone is the natural hormone; a progestin or progestogen is a synthetic one, and levonorgestrel belongs to the family derived structurally from testosterone. Pills come in two designs — combined pills carrying an oestrogen plus a progestogen, and progestogen-only pills used where oestrogen is unsuitable, as during breastfeeding — and the same hormones are delivered by injection, implant and intrauterine device as well. India adds a distinctive chapter to this chemistry: centchroman, or ormeloxifene, is a non-steroidal selective oestrogen receptor modulator taken twice weekly for the first twelve weeks and once a week thereafter, discovered at the Central Drug Research Institute in Lucknow and marketed from 1991 as Saheli.

State PCS 2025 Q135 — Science & Technology PYQ with Answer

State PCS 2025 Q135 — Science & Technology PYQ with Answer