A drug that causes increased severity of Parkinson-like symptoms is most likely to be which type?

A drug that causes increased severity of Parkinson-like symptoms is most likely a dopamine antagonist. This class of medications works by blocking dopamine receptors in the brain. Since Parkinson's disease is characterized by a deficiency of dopamine in certain areas of the brain, particularly the substantia nigra, the action of dopamine antagonists can exacerbate motor symptoms associated with the disease, such as rigidity, bradykinesia, and tremors.

Dopamine receptors are crucial for the regulation of movement and coordination; hence, when these receptors are antagonized, it leads to greater difficulties in movement, mimicking or worsening Parkinsonian symptoms. This worsening occurs because the blockade of dopamine leads to an imbalance between dopaminergic and cholinergic systems in the basal ganglia, which is crucial for motor control.

In contrast, dopamine agonists would stimulate dopamine receptors and may alleviate symptoms of Parkinson's, while serotonin agonists and antagonists primarily affect serotonin receptors and do not have a direct role in the motor symptoms typical of Parkinson’s disease. This distinction underscores why a dopamine antagonist is the type of drug most likely to exacerbate Parkinson-like symptoms.