**Core Concept**
Centchroman, also known as Ormeloxifene, is a synthetic non-steroidal selective estrogen receptor modulator (SERM) used as a contraceptive. It works by inhibiting estrogen receptors in the endometrium, which leads to a decrease in estrogen levels and subsequent reduction in endometrial proliferation.

**Why the Correct Answer is Right**
Centchroman is generally contraindicated in patients with liver disease due to its potential to cause liver function abnormalities and hepatotoxicity. This is because centchroman is metabolized by the liver and can accumulate in patients with liver dysfunction, leading to adverse effects.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is correct, as centchroman is indeed a synthetic non-steroidal contraceptive.

**Option B:** This option is incorrect because centchroman can cause a range of side effects, including oligomenorrhoea, but also other symptoms such as headaches, dizziness, and nausea.

**Option D:** This option is correct, as centchroman can be used as a post-coital pill to prevent pregnancy after unprotected sex.

**Clinical Pearl / High-Yield Fact**
Centchroman is a unique contraceptive option that can be used for both pre- and post-coital contraception, but it is contraindicated in patients with liver disease due to its potential for hepatotoxicity.

**✓ Correct Answer: C. Safe in liver disease**