Dopamine depletion in the basal ganglia leads to motor dysfunction. In Parkinson disease neuronal degeneration is idiopathic. In secondary causes of parkinsonism, the mechanism is interference with dopamine action in the basal ganglia. Dopamine-blocking medications are a common cause of secondary parkinsonism.

Besides dopamine-blocking medications, secondary causes of parkinsonism include neurodegenerative disorders (e.g., Lewy body dementia), cerebrovascular disease, tumors (rare), and encephalitis (usually transient).

Drug-induced parkinsonism (DIP) usually occurs within days to weeks after starting antipsychotics though can occur later. There is no clear dose–effect relationship [1]. The tremor is often less prominent than other symptoms of parkinsonism such as muscle stiffness, bradykinesia, and shuffling gait. As compared to Parkinson disease, the tremor in DIP is more likely to be postural, bilateral, symmetrical, and commonly affects females. Tremor in Parkinson disease occurs at rest, is unilateral, and commonly affects males. But unfortunately, in a large number of cases, DIP presents with features similar to Parkinson disease and the two are not clearly distinguishable. Due to the difficulties in diagnosis, the exact prevalence of DIP is uncertain .

DIP usually resolves within weeks to months of stopping the medication though symptom persistence has been reported [2]. The symptom persistence is reported to be as high as 50% and recurrence of symptoms was reported in 7% patients on long-term follow-up [2]. These cases may reflect underlying Parkinson disease with DIP being a precipitant.

The risk of DIP with different antipsychotic medications correlates with their overall risk of extrapyramidal symptoms. Typical antipsychotics carry a higher risk than atypical agents, though the risk with lower potency typical agents is equivalent to atypical agents. Among atypical antipsychotics, clozapine and quetiapine are the least likely to cause DIP. Even aripiprazole , a partial dopamine agonist, is associated with DIP. Other agents that act by blocking dopamine, such as metoclopramide, can cause DIP. Rarely, lithium, antidepressants, and antiepileptic agents can cause DIP after long-term use due to poorly understood mechanisms.