Haloperidol is an antipsychotic drug that has similar actions to the antipsychotic medicine phenothiazine.
The drug works as an inverse agonist of dopamine, a chemical in the brain involved in thinking, feeling and behavior. Haloperidol is classified as a highly potent neuroleptic, meaning it relieves nervous tension through the depression of nerve function.
Haloperidol is around fifty times stronger than chlorpromazine, the first antipsychotic drug that was developed in 1950.
Haloperidol has shown beneficial effects in the treatment of delusions and hallucinations. These effects are mainly achieved through blockage of dopamine receptors in the mesocortex and limbic system.
Haloperidol prevents the effects of dopamine in the nigrostriatal pathways, which probably explains the associated side effects such as akathisia and dystonias. However, the agent only has mild antihistaminic and anticholinergic properties, meaning side effects such as hypotension, constipation and dry mouth occur less frequently than when neuroleptics such as chlorpromazine are used.
The specific actions of haloperidol in the limbic system also reduce psychomotor agitation, therefore providing a sedative effect. On the other hand, the drug’s potent antagonism of dopamine receptors may also worsen this agitation. In particular, blockage of the D2 receptor can lead to anxiety, agitation, akathisia and restlessness.
Haloperidol also acts as a potent antiemetic, owing to its peripheral antidopaminergic effects on the chemoreceptor trigger zone (CTZ) in the brain. The drug can therefore be used to relieve nausea and sickness that occur as side effects of chemotherapy.