**Core Concept**
Tardive dyskinesia is a side effect of long-term antipsychotic medication use, characterized by involuntary, repetitive movements, often of the face and extremities. However, acute dystonic reactions, also known as toicollis, are a different type of movement disorder that can occur within the first few days of antipsychotic therapy.

**Why the Correct Answer is Right**
Acute dystonic reactions are caused by the blockade of dopamine receptors in the nigrostriatal pathway, leading to an imbalance between dopamine and acetylcholine. The most effective treatment for acute dystonic reactions is the administration of anticholinergic medications, such as benztropine or diphenhydramine, which counteract the effects of excessive acetylcholine activity.

**Why Each Wrong Option is Incorrect**
**Option A:** Haloperidol is the antipsychotic medication that likely caused the toicollis, so administering more of the same medication would not be an effective treatment.
**Option B:** Benzodiazepines, such as diazepam, may provide some relief from anxiety or agitation but are not the primary treatment for acute dystonic reactions.
**Option C:** Propranolol is a beta-blocker that may be used to treat other types of movement disorders, such as essential tremor, but is not the first-line treatment for acute dystonic reactions.

**Clinical Pearl / High-Yield Fact**
The "tardive" in tardive dyskinesia refers to the delayed onset of the movement disorder, usually occurring after several months or years of antipsychotic therapy. In contrast, acute dystonic reactions occur within the first few days of treatment.

**Correct Answer:** D. Diphenhydramine (an anticholinergic medication)