Evidence-Based Reviews

Antipsychotics, dopamine, and pain

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Haloperidol is prescribed widely by nonpsychiatrists, primarily to treat agitation. Intravenous haloperidol has been used for the abortive treatment of headaches.18 Paradoxically, IV haloperidol is less likely to induce extrapyramidal symptoms (EPS) than the oral formulation because of a more pronounced anticholinergic action in IV use. Haloperidol can help relieve gastroparesis and nausea, especially in IV administration,19 but prolonged oral administration is associated with unwanted movement problems and should be avoided.20

Chlorpromazine is more anticholinergic than haloperidol. It can be used in the abortive treatment of headaches (preferably via IV and IM administration), nausea, hiccups, porphyria, and serotonin syndrome, but it is very sedating and frequently produces hypotension, dangerous QT prolongation, and sensations of thought-blocking.21

Pimozide is reported to help with skin picking, trichotillomania, and somatic hallucinations.22

Droperidol, promethazine, and prochlorperazine are used off-label to treat nausea and headaches. Primary care clinicians may not be aware that these commonly used medications are antipsychotics. Similar to other FGAs, these 3 agents may produce NMS and tardive dyskinesia (TD). The same applies to the prokinetic drug metoclopramide.

Second-generation antipsychotics used for nonpsychiatric conditions

Second-generation antipsychotics

Second-generation antipsychotics (SGAs) work with various serotonin receptors, offsetting and enhancing the antipsychotic function of dopamine blockade. This diminishes but does not eliminate EPS and the risk of TD. Fortunately, the risk of NMS is lower with SGAs than with FGAs. Many SGAs are FDA-approved for treating schizophrenia and other psychiatric disorders, and some have relevance for pain management (Table 3). Many SGAs help with depressive symptoms and are powerful mood stabilizers. As such, they may diminish central over-firing of dopaminergic and serotonergic neurons involved in the pain cascade, which in turn decreases pain transmission and perception. The downside is that in general, SGAs increase the risk of diabetes and hyperlipidemia.

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