What is the molecular mechanism of action of benzodiazepines?

The molecular mechanism of benzodiazepines involves stimulation of specific allosteric benzodiazepine receptors linked to the $\gamma$-subunit of the supramolecular $GABA_A$ receptor complex. This leads to allosteric modulation of the GABA receptor, increasing its sensitivity to the neurotransmitter GABA and increasing the frequency of chloride channel openings. As a result, there is a massive influx of $Cl^-$ ions into the neuron, membrane hyperpolarization, and the development of neuronal inhibition.

What are the specific side effects of Z-drugs?

Specific side effects of zopiclone include a bitter, metallic taste in the mouth. Gastrointestinal disturbances such as abdominal pain, diarrhea, and nausea are also possible. Upon awakening, post-somnic effects may occur, including dizziness and impaired coordination.

Which histamine $H_1$ receptor blockers are used as hypnotics?

Histamine $H_1$ receptor blockers capable of crossing the blood-brain barrier and exerting a depressive effect on the central nervous system are used as hypnotics. Representatives of this group include the dedicated hypnotic doxylamine, as well as diphenhydramine, which is primarily an anti-allergic agent but possesses a pronounced hypnotic effect.

What is the difference between narcotic and non-narcotic types of action?

The narcotic type of action (e.g., in barbiturates) causes total, non-selective CNS depression. The non-narcotic type acts more subtly, selectively suppressing only individual brain structures.

How do hypnotics alter the REM sleep phase?

Most hypnotic medications increase the latency period (time to onset) of the REM sleep phase and shorten its total duration, making sleep non-physiological.

What happens during abrupt drug withdrawal?

A compensatory 'rebound phenomenon' develops. The duration of REM sleep sharply lengthens, leading to nightmares, an abundance of dreams, and frequent awakenings.

Home › Pharmacology › Hypnotics (Sleep Medications)

Hypnotics

Hypnotica

For medical students2 min readUpdated 2026-10-10

Hypnotics (Hypnotica) are a group of pharmacological agents whose primary target is to facilitate sleep onset and increase total sleep duration. Depending on the dose and chemical structure, these drugs can induce effects ranging from mild sedation to profound central nervous system depression.

Dose-dependenceAt low doses, hypnotic drugs exhibit sedative (calming) effects.

MechanismBased on the inhibition of synaptic transmission in the CNS (selective or non-selective).

Drug selectionThe main criterion for prescription is the required duration of action.

Withdrawal syndromeAbrupt cessation of intake causes a 'rebound phenomenon' with nightmares.

Principles of Action and Effects on the CNS

The action of hypnotic drugs is dose-dependent. The fundamental mechanism involves the inhibition of synaptic transmission in the nervous system. Based on the selectivity of this inhibition, two types of action are distinguished:

Non-narcotic type. Characterized by a relatively selective effect: the drugs suppress only specific structures and functions of the brain.
Narcotic type. Leads to a generalized, total, and non-selective depression of the central nervous system.

Classification of Hypnotic Agents

The systematic classification of these drugs is based on their chemical structure and type of action on the central nervous system.

1. Drugs with a non-narcotic type of action:

Benzodiazepine receptor agonists. Include classical benzodiazepine derivatives (nitrazepam, flunitrazepam, triazolam, midazolam) and non-benzodiazepine Z-drugs (zopiclone, zolpidem, zaleplon).
Histamine $H_1$ receptor blockers. A typical representative is doxylamine.
Melatonin receptor agonists. This group includes ramelteon.

2. Drugs with a narcotic type of action:

Barbituric acid derivatives (barbiturates). The main representative is phenobarbital.
Aliphatic compounds. This group includes chloral hydrate.

Effects on Sleep Architecture (Pharmacodynamics)

It is important to understand that drug-induced sleep differs from natural (physiological) sleep. Primarily, the rapid eye movement (REM) sleep phase is distorted. Under the influence of these drugs, its latency period (time to onset) increases and its total duration significantly decreases.

Different drug groups disrupt the ratio of REM to non-REM sleep to varying degrees:

Pronounced disruption: barbituric acid derivatives.
Moderate disruption: benzodiazepines (alter sleep architecture to a lesser extent than barbiturates).
Minimal impact: zolpidem and zopiclone alter the structure very little, while chloral hydrate has virtually no effect on it, providing the most physiological sleep.

Withdrawal Syndrome ("Rebound Phenomenon")

Upon abrupt cessation of hypnotics, a compensatory reaction of the nervous system occurs. Sleep phases shift again: the REM sleep latency period sharply shortens, and its duration increases abnormally.

Clinically, this condition manifests as significant discomfort for the patient. Frequent night awakenings, an abundance of vivid dreams, and severe nightmares occur.

Requirements for Modern Drugs

To date, a drug that fully meets the criteria of an 'ideal' hypnotic does not exist. However, clear requirements have been established for such agents:

Pharmacokinetics: Ensuring rapid sleep onset and maintaining optimal sleep duration.
Physiological profile: Lack of interference with sleep architecture (preserving the natural ratio of phases).
Safety: Absence of respiratory center depression and negative effects on the patient's memory.
Lack of dependence: Low risk of developing tolerance ( habituation), and exclusion of physical and psychological drug dependence formation.

Mnemonic

Remembering modern non-benzodiazepine agonists (Z-drugs) is easy: they all start with the letter 'Z' (Zopiclone, Zolpidem, Zaleplon), just like the sleep symbol 'Z-z-z...'.

Frequently asked questions

What is the molecular mechanism of action of benzodiazepines?: The molecular mechanism of benzodiazepines involves stimulation of specific allosteric benzodiazepine receptors linked to the $\gamma$-subunit of the supramolecular $GABA_A$ receptor complex. This leads to allosteric modulation of the GABA receptor, increasing its sensitivity to the neurotransmitter GABA and increasing the frequency of chloride channel openings. As a result, there is a massive influx of $Cl^-$ ions into the neuron, membrane hyperpolarization, and the development of neuronal inhibition.
What are the specific side effects of Z-drugs?: Specific side effects of zopiclone include a bitter, metallic taste in the mouth. Gastrointestinal disturbances such as abdominal pain, diarrhea, and nausea are also possible. Upon awakening, post-somnic effects may occur, including dizziness and impaired coordination.
Which histamine $H_1$ receptor blockers are used as hypnotics?: Histamine $H_1$ receptor blockers capable of crossing the blood-brain barrier and exerting a depressive effect on the central nervous system are used as hypnotics. Representatives of this group include the dedicated hypnotic doxylamine, as well as diphenhydramine, which is primarily an anti-allergic agent but possesses a pronounced hypnotic effect.
What is the difference between narcotic and non-narcotic types of action?: The narcotic type of action (e.g., in barbiturates) causes total, non-selective CNS depression. The non-narcotic type acts more subtly, selectively suppressing only individual brain structures.
How do hypnotics alter the REM sleep phase?: Most hypnotic medications increase the latency period (time to onset) of the REM sleep phase and shorten its total duration, making sleep non-physiological.
What happens during abrupt drug withdrawal?: A compensatory 'rebound phenomenon' develops. The duration of REM sleep sharply lengthens, leading to nightmares, an abundance of dreams, and frequent awakenings.

Go deeper

Mechanisms of drug tolerance and dependence formation
Characteristics of respiratory center depression in overdose
Effects of hypnotics on cognitive functions and memory
Specific receptor targets of benzodiazepines and Z-drugs