**Core Concept**
Isoniazid, ethambutol, rifampicin, and pyrazinamide are first-line antitubercular drugs used to treat tuberculosis (TB). Isoniazid and pyrazinamide are especially prone to causing hepatotoxicity, while rifampicin is known for its effect on the thyroid axis.

**Why the Correct Answer is Right**
Pyrazinamide is associated with hypothyroidism due to its impact on thyroid function. This is thought to be mediated by the inhibition of peripheral conversion of thyroxine (T4) to triiodothyronine (T3) in the liver, as well as interference with thyroid hormone release. The exact mechanism is still not fully understood, but it's believed to be related to the drug's ability to inhibit the enzyme dihydroorotate dehydrogenase, which is also involved in thyroid hormone synthesis.

**Why Each Wrong Option is Incorrect**
**Option A:** Isoniazid is associated with peripheral neuropathy and hepatotoxicity, but it's not typically linked to hypothyroidism.
**Option B:** Ethambutol is known for its potential to cause optic neuritis, but it does not have a significant association with thyroid function.
**Option C:** Rifampicin is a potent inducer of the cytochrome P450 enzyme system, which can affect the metabolism of many drugs, but it's not typically associated with hypothyroidism.

**Clinical Pearl / High-Yield Fact**
It's essential to note that pyrazinamide-induced hypothyroidism is often asymptomatic and may only be detected through routine thyroid function tests. Monitoring of thyroid function is recommended in patients taking pyrazinamide, especially if they have a history of thyroid disease.

**Correct Answer:** C. Pyrazinamide