**Core Concept**
Drug-induced Parkinsonism is a condition characterized by parkinsonian symptoms, such as tremor, rigidity, and bradykinesia, caused by the use of certain medications, particularly antipsychotics and antidepressants. The underlying mechanism involves blockade of dopamine receptors in the nigrostriatal pathway, leading to an imbalance between dopaminergic and cholinergic neurotransmission.

**Why the Correct Answer is Right**
The drug of choice in drug-induced Parkinsonism is a dopamine agonist, specifically **pramipexole** or **ropinirole**, which directly stimulates dopamine receptors in the striatum, counteracting the effects of dopamine receptor blockade caused by the offending medication. These dopamine agonists mimic the action of dopamine in the brain, thereby reducing parkinsonian symptoms.

**Why Each Wrong Option is Incorrect**
**Option A:** **Benzhexol (Trihexyphenidyl)** is an anticholinergic agent, which may exacerbate drug-induced Parkinsonism by further reducing dopaminergic activity. **Option B:** **Levodopa** is a precursor to dopamine, but its use in drug-induced Parkinsonism is not the first line of treatment, and it can have significant side effects. **Option C:** **Metoclopramide** is an antiemetic that can cause extrapyramidal side effects, including Parkinsonism, and is not used to treat it.

**Clinical Pearl / High-Yield Fact**
Dopamine agonists, such as pramipexole and ropinirole, are preferred over anticholinergic agents and levodopa in the treatment of drug-induced Parkinsonism due to their efficacy and lower risk of side effects.

**Correct Answer:** D. Metoclopramide