Large doses of
chlorpromazine may reduce or even abolish the antihypertensive effects of
guanethidine. The antihypertensive effects of
guanethidine can be reduced by
haloperidol and thiothixene. However, in some patients the hypotensive effect of
chlorpromazine may predominate. Note also, that the
antipsychotics can cause postural hypotension.
Increases or decreases in blood pressure may occur as a result of concurrent use. Monitor blood pressure adjusting the
guanethidine dose as necessary.