What is the molecular mechanism of the antipsychotic action of typical neuroleptics?

The molecular mechanism of typical antipsychotics involves the blockade of postsynaptic dopamine $D_2$ receptors in the central nervous system. The primary site of action is the mesolimbic pathway of the brain. Through this mechanism, the drugs primarily eliminate positive symptoms of psychosis, such as delusions and hallucinations. At the same time, they have virtually no effect on negative symptoms or cognitive impairment.

What is the pathogenetic mechanism of hyperprolactinemia development during treatment with typical antipsychotics?

The pathogenesis of hyperprolactinemia is driven by the blockade of dopamine $D_2$ receptors in the tuberoinfundibular pathway, which connects the hypothalamus to the pituitary gland. Under normal conditions, dopamine acts as a prolactin-inhibiting factor. Receptor blockade by typical neuroleptics removes this physiological inhibitory tone on the anterior pituitary, leading to increased prolactin secretion. Clinically, this endocrine abnormality may manifest as galactorrhea in women, gynecomastia in men, and suppressed gonadotropin production leading to amenorrhea and impotence.

Which receptors are predominantly blocked by atypical antipsychotics?

Atypical antipsychotics predominantly block serotonin 5-$HT_{2A}$ and dopamine $D_2$ receptors. They are characterized by a high ratio of 5-$HT_{2A}$ to $D_2$ receptor blockade. Their receptor profile also includes alpha-adrenergic and $H_1$ histamine receptor antagonism, with virtually no affinity for muscarinic receptors. The blockade of 5-$HT_{2A}$ receptors reciprocally increases dopaminergic activity in the nigrostriatal pathway, which compensates for $D_2$ blockade and reduces the risk of extrapyramidal symptoms.

What is the mechanism of the antiemetic action of typical antipsychotics?

The antiemetic mechanism of typical antipsychotics is due to the blockade of dopamine $D_2$ receptors located in the chemoreceptor trigger zone (CTZ) of the vomiting center. This area is situated on the floor of the fourth ventricle in the medulla oblongata and lacks a true blood-brain barrier. By inhibiting $D_2$ receptors in this region, typical antipsychotics block the transmission of impulses triggered by circulating toxins or emetic agents in the blood or cerebrospinal fluid, thereby suppressing the vomiting reflex.

What is the main difference between typical and atypical antipsychotics?

Typical antipsychotics carry a high risk of causing extrapyramidal symptoms (parkinsonism, dystonia) at therapeutic doses, whereas this phenomenon is uncommon with atypical agents.

Which drug is more potent in its antipsychotic action: haloperidol or chlorpromazine?

Haloperidol surpasses chlorpromazine in antipsychotic potency. Additionally, chlorpromazine possesses stronger antimuscarinic activity.

Why do typical antipsychotics cause galactorrhea?

Galactorrhea occurs due to hyperprolactinemia—an endocrine disturbance induced by the action of drugs in this class.

Home › Pharmacology › Antipsychotics: Classification and Mechanisms

Antipsychotics

Antipsychotica

For medical students2 min readUpdated 2026-10-10

Antipsychotics (neuroleptics) are divided into two main groups—typical and atypical—which differ in their mechanisms of action and the risk of side effects. They are widely used in psychiatric practice and exhibit potent antipsychotic efficacy.

Main GroupsTypical and atypical antipsychotics

Typical DrugsHaloperidol, chlorpromazine, droperidol

Atypical DrugsClozapine, risperidone, olanzapine

Side EffectsExtrapyramidal symptoms and hyperprolactinemia

Classification of Antipsychotic Drugs

Drugs in this category are divided into two major groups based on their mechanism of action and side effect profile:

"Typical" Antipsychotics: Classical representatives of the group, including haloperidol, chlorpromazine, fluphenazine, droperidol, thioridazine, and chlorprothixene.
"Atypical" Antipsychotics: Modern agents, which include clozapine, risperidone, olanzapine, and aripiprazole.

Pharmacological Profile of Typical Antipsychotics

Traditional antipsychotics possess strong antipsychotic activity and a pronounced antiemetic effect. In addition, they can potentiate (i.e., enhance) the effects of general anesthetics and opioid analgesics.

The main hallmark of typical agents is a high risk of developing extrapyramidal symptoms (EPS) (such as parkinsonism, dystonia, and dyskinesia), which serve as a marker for this group (and are particularly prominent with haloperidol and chlorpromazine). They also cause endocrine disorders in the form of hyperprolactinemia, which may manifest as galactorrhea.

Features of Chlorpromazine

Chlorpromazine occupies a unique place among typical antipsychotics due to its pharmacological properties:

It exhibits marked anticholinergic (antimuscarinic) activity, setting it apart from haloperidol, in which this effect is much weaker.
It affects the autonomic nervous system through alpha-blocking and antimuscarinic actions.
It can cause galactorrhea due to elevated prolactin levels.
It is less potent in its antipsychotic effect compared to haloperidol.

Features of Atypical Antipsychotics

The main difference between atypical agents (such as olanzapine, aripiprazole, and clozapine) is that extrapyramidal symptoms are not typical when used at therapeutic doses.

Unlike classical typical agents, these drugs demonstrate higher efficacy against the "negative" symptoms of psychoses, such as social withdrawal and apathy.

Mnemonic

Typical drugs are "troublesome" regarding the extrapyramidal pathway (causing extrapyramidal symptoms), while atypical drugs are "accommodating" (lacking these side effects at therapeutic doses).

Frequently asked questions

What is the molecular mechanism of the antipsychotic action of typical neuroleptics?: The molecular mechanism of typical antipsychotics involves the blockade of postsynaptic dopamine $D_2$ receptors in the central nervous system. The primary site of action is the mesolimbic pathway of the brain. Through this mechanism, the drugs primarily eliminate positive symptoms of psychosis, such as delusions and hallucinations. At the same time, they have virtually no effect on negative symptoms or cognitive impairment.
What is the pathogenetic mechanism of hyperprolactinemia development during treatment with typical antipsychotics?: The pathogenesis of hyperprolactinemia is driven by the blockade of dopamine $D_2$ receptors in the tuberoinfundibular pathway, which connects the hypothalamus to the pituitary gland. Under normal conditions, dopamine acts as a prolactin-inhibiting factor. Receptor blockade by typical neuroleptics removes this physiological inhibitory tone on the anterior pituitary, leading to increased prolactin secretion. Clinically, this endocrine abnormality may manifest as galactorrhea in women, gynecomastia in men, and suppressed gonadotropin production leading to amenorrhea and impotence.
Which receptors are predominantly blocked by atypical antipsychotics?: Atypical antipsychotics predominantly block serotonin 5-$HT_{2A}$ and dopamine $D_2$ receptors. They are characterized by a high ratio of 5-$HT_{2A}$ to $D_2$ receptor blockade. Their receptor profile also includes alpha-adrenergic and $H_1$ histamine receptor antagonism, with virtually no affinity for muscarinic receptors. The blockade of 5-$HT_{2A}$ receptors reciprocally increases dopaminergic activity in the nigrostriatal pathway, which compensates for $D_2$ blockade and reduces the risk of extrapyramidal symptoms.
What is the mechanism of the antiemetic action of typical antipsychotics?: The antiemetic mechanism of typical antipsychotics is due to the blockade of dopamine $D_2$ receptors located in the chemoreceptor trigger zone (CTZ) of the vomiting center. This area is situated on the floor of the fourth ventricle in the medulla oblongata and lacks a true blood-brain barrier. By inhibiting $D_2$ receptors in this region, typical antipsychotics block the transmission of impulses triggered by circulating toxins or emetic agents in the blood or cerebrospinal fluid, thereby suppressing the vomiting reflex.
What is the main difference between typical and atypical antipsychotics?: Typical antipsychotics carry a high risk of causing extrapyramidal symptoms (parkinsonism, dystonia) at therapeutic doses, whereas this phenomenon is uncommon with atypical agents.
Which drug is more potent in its antipsychotic action: haloperidol or chlorpromazine?: Haloperidol surpasses chlorpromazine in antipsychotic potency. Additionally, chlorpromazine possesses stronger antimuscarinic activity.
Why do typical antipsychotics cause galactorrhea?: Galactorrhea occurs due to hyperprolactinemia—an endocrine disturbance induced by the action of drugs in this class.

Go deeper

Detailed receptor profile of chlorpromazine and its effects on the autonomic nervous system
Comparison of antiemetic potency among various typical antipsychotics
Mechanisms of hyperprolactinemia development and clinical manifestations of endocrine disorders
Pharmacodynamics of atypical antipsychotics (olanzapine, aripiprazole, clozapine) regarding negative symptoms
Potentiation of general anesthetics and opioid analgesics by typical antipsychotics