**Core Concept**
Oestrogenic effects can be a side effect of certain medications used to treat peptic ulcers, leading to gynaecomastia. This is due to the increased levels of oestrogen or oestrogen-like substances in the body.

**Why the Correct Answer is Right**
Cimetidine, a histamine H2-receptor antagonist, is known to cause gynaecomastia in some patients due to its anti-androgenic effects. It inhibits the enzyme cytochrome P450, which is involved in the metabolism of testosterone, leading to increased levels of oestrogen. This results in an imbalance between oestrogen and testosterone, causing gynaecomastia.

**Why Each Wrong Option is Incorrect**
**Option A:** Ranitidine is another histamine H2-receptor antagonist, but it is less likely to cause gynaecomastia compared to cimetidine. It does not have the same level of anti-androgenic effects.
**Option B:** Omeprazole is a proton pump inhibitor, which works by inhibiting the H+/K+ ATPase enzyme in the gastric parietal cells. It does not have any significant anti-androgenic effects.
**Option C:** Sucralfate is a protective agent that forms a complex with the ulcer site, protecting it from acid and pepsin. It does not have any significant hormonal effects.

**Clinical Pearl / High-Yield Fact**
Cimetidine is not only associated with gynaecomastia but also with other hormonal side effects, such as impotence and galactorrhea.

**Correct Answer: C. Cimetidine**