Dopamine blockers, side-effects

Drugs that are successful in treating the disease act as dopamine receptor blockers and are known as antipsychot-ics or neuroleptics (e.g. chlorpromazine, haloperidol). Antipsychotic drags reduce some of the symptoms, especially the delusions and hallucinations. A side-effect of the drugs is that they can result in symptoms similar to those seen in patients with Parkinson s disease. This is not surprising, since the hypothesis to explain Parkinson s disease is too low a concentration of dopamine in a specific area of the brain (see below). 

The first generation antipsychotics, now known as typical drugs, were all D2 receptor blockers and, as such, very likely to produce Parkinsonian side effects. Because antipsychotic potency was associated with D2 receptor affinity, it was assumed that dopamine overactivity was the essential defect in schizophrenia and that a direct dopamine blockade was the definitive route to treatment. But these drugs affected both the target dopamine pathways of the mesolimbic projection and the uninvolved nigrostriatal projection. Unfortunately, that meant that movement disorders were the price that had to be paid for antipsychosis. 

Other, chemically distinct dopamine blockers were then developed, such as thiothixene, haloperidol, loxapine, molindone, and pimozide. All of these antipsychotics are potent dopamine blockers and collectively were called neuroleptics because they inadvertently cause certain neurological side effects (discussed below). More recently, atypical antipsychotic medications have been developed (clozapine and risperidone), which are effective antipsychotics yet are weak dopamine blockers and cause minimal neurological side effects. This group is discussed separately below. 

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