**Core Concept**
Centchroman, also known as Ormeloxifene, is a non-steroidal selective estrogen receptor modulator (SERM) used as a contraceptive and for the treatment of dysmenorrhea and menstrual disorders. Its mechanism of action involves binding to estrogen receptors, thereby exerting both agonist and antagonist effects on estrogen-responsive tissues.

**Why the Correct Answer is Right**
Centchroman acts by inhibiting the growth and proliferation of endometrial tissue, leading to a thinning of the endometrium and decreased menstrual bleeding. It also has a weak estrogenic effect on the breasts, which may contribute to its contraceptive efficacy. By modulating estrogen receptors, centchroman disrupts the normal menstrual cycle, preventing ovulation and fertilization.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because the correct dose of centchroman is not provided in this option.
**Option B:** Incorrect because the specified dose is not accurate for centchroman.
**Option C:** Incorrect because the given dose is not the recommended dose for centchroman.

**Clinical Pearl / High-Yield Fact**
Centchroman is a unique contraceptive option that can be taken orally for a short duration, typically 30 days, to prevent pregnancy. It has a favorable side-effect profile and can be used in women with a history of thromboembolic disorders, making it a suitable choice for certain patient populations.

**Correct Answer: D. 30 mg twice a day for 30 days.**