Drugs, Brain and Behaviour (14) - Sedative-Hypnotics: Alcohol

Sedative-hypnotics

A class of CNS depressants that reduce neural activity and produce sedation

Examples of sedative-hypnotics

Alcohol, barbiturates, and benzodiazepines.

Alcohol classification

A sedative-hypnotic and anxiolytic CNS depressant.

Key property of sedative-hypnotics

Reduce central nervous system activity.

Additive effects

Combined use increases overall drug effects.

Cross-tolerance

Tolerance to one drug reduces response to others in the same class.

Ethanol

The type of alcohol consumed in beverages.

Toxic alcohols

Methanol and isopropanol are highly dangerous and not safe for consumption

Methanol toxicity

Converted into formaldehyde causing blindness and death.

Fermentation

Process where yeast converts sugar into ethanol and CO₂.

Examples of fermentation sources

Grapes (wine), grains (beer/whisky), rice (sake).

Limitation of fermentation

Alcohol concentration cannot exceed ~15% due to yeast death.

Distillation

Process of concentrating alcohol by heating and condensing vapour

Examples of distilled drinks

Whisky, vodka, rum, and brandy.

History of alcohol use

Dates back to prehistoric times (~8000 BC).

Effect of distillation on use

Increased availability and consumption of strong alcohol.

Temperance movement

Social movement promoting abstinence from alcohol.

Prohibition

Ban on alcohol production and sale (e.g., in the US).

Effect of prohibition

Increased crime, poisoning, and use of stronger substances.

Binge drinking

5+ drinks (men) or 4+ drinks (women) in one session.

Perception issue

Many heavy drinkers do not recognise problematic use.

Blood alcohol content (BAC)

Grams of alcohol per 100 ml of blood.

Legal driving limit

0.08 BAC in England and Wales.

BAC 0.2–0.3

Severe intoxication.

BAC 0.35–0.5

Potentially fatal range.

Margin of safety

Alcohol has a low margin of safety.

Behavioural effects of alcohol

Impairs judgement, reaction time, and coordination.

Drunk driving risk

Increased due to poor judgement and slower reactions.

Alcohol absorption

Mainly occurs in the small intestine.

Factors increasing absorption

High concentration and empty stomach.

Factors decreasing absorption

Presence of food.

Alcohol distribution

Travels throughout blood, brain, and body tissues.

Alcohol elimination

About 10% excreted unchanged in breath, sweat, and urine.

Alcohol metabolism

Mainly occurs in liver via alcohol dehydrogenase (ADH).

Breathalyser

Device estimating BAC through breath alcohol levels.

Acute tolerance

Reduced drug effect within a single drinking session.

Chronic tolerance

Reduced effect after repeated alcohol use.

Metabolic tolerance

Increased enzyme activity breaking down alcohol faster.

Pharmacodynamic tolerance

Brain adapts to alcohol’s effects.

Hangover

After-effect caused by dehydration, low glucose, and acetaldehyde buildup.

Hangover as withdrawal

Drinking again relieves symptoms, indicating mild withdrawal.

Alcohol withdrawal

Includes anxiety, tremors, and seizures.

Vasodilation

Alcohol widens blood vessels causing flushed skin.

False warmth effect

Increased heat loss raises risk of hypothermia.

Antidiuretic hormone inhibition

Leads to increased urination.

Alcohol and sleep

Helps sleep onset but disrupts REM sleep.

REM rebound

Increased dreaming during withdrawal.

GABA-A receptor

Ionotropic receptor enhanced by alcohol.

Effect on GABA

Increased Cl⁻ influx leading to neuronal inhibition.

Glutamate system effect

Alcohol inhibits NMDA receptors.

NMDA inhibition

Reduces excitatory signalling and impairs memory.

Other alcohol targets

Calcium channels, glycine, nicotinic, and serotonin receptors.

Alcohol and dopamine

Increases dopamine in nucleus accumbens.

Mechanism of dopamine increase

Via β-endorphin release and reduced GABA inhibition.

Alcohol reward pathway

Involves dopamine activation in reward circuits.

Self-administration challenge

Animals do not readily drink alcohol due to taste and slow onset.

Sucrose fading

Gradual method to train animals to drink alcohol.

Intravenous self-administration

Animals will self-administer alcohol directly.

Binge-like behaviour in animals

Can model human drinking patterns.

Cirrhosis

Severe liver damage caused by chronic alcohol use.

Effect of cirrhosis

Loss of liver function due to scarring.

Korsakoff syndrome

Brain disorder caused by vitamin B1 deficiency.

Symptoms of Korsakoff syndrome

Memory loss and confusion.

Other chronic risks

Cardiovascular disease and immune suppression.

Fetal alcohol syndrome (FAS)

Developmental disorder caused by prenatal alcohol exposure.

FAS effects

Reduced brain size, low birth weight, cognitive deficits.

Mechanism of fetal damage

Alcohol induces apoptosis during brain development.

Placental transfer

Alcohol crosses placenta and affects fetus.

Absinthe

Alcoholic drink containing wormwood extract.

Thujone

Compound in absinthe acting as a GABA-A antagonist.

Effect of thujone

Can cause seizures at high doses.

Misconception about absinthe

Hallucinations mainly due to alcohol, not thujone.

Core mechanism of alcohol

Enhances GABA and inhibits glutamate signalling.

Key behavioural effects

Sedation, impaired cognition, and motor impairment.

Key risks of alcohol

Overdose, organ damage, and developmental harm.

Repeated alcohol use

Leads to tolerance, dependence, and withdrawal.