The actions of serotonin, like those of histamine, can be antagonized in several ways. Such antagonism is clearly desirable in those rare patients who have carcinoid tumor and may also be valuable in certain other conditions.
As noted, serotonin synthesis can be inhibited by p-chlorophenylalanine and p-chloroamphetamine. However, these
agents are too toxic for general use. Storage of serotonin can be inhibited by the use of reserpine, but the sympatholytic effects of this drug and the high levels of circulating serotonin that result from release prevent its use in carcinoid. Therefore, receptor blockade is the major therapeutic approach to conditions of serotonin excess.