Ethanol and toxic alcohols
How alcohol acts and harms, how withdrawal is recognised and treated, and why methanol and ethylene glycol poisonings need an antidote and dialysis.
Ethanol is a toxic, psychoactive, dependence-producing substance that is also the most widely used drug in the world. Methanol and ethylene glycol are alcohols found in industrial and household products and in adulterated drinks; they are dangerous because the body converts them into acids that injure the eyes, kidneys and brain.
Ethanol's effects
Ethanol enhances GABA and blocks glutamate signalling, so it sedates, impairs judgement and coordination and, at high levels, depresses breathing. Combined with opioids or other sedatives it raises the risk of fatal overdose. WHO describes alcohol as a cause of liver and heart disease, several cancers, depression, injuries and harm in pregnancy such as fetal alcohol spectrum disorders.
Withdrawal
After long heavy use the brain adapts, and stopping suddenly unmasks overactivity: tremor, sweating, anxiety, insomnia, fast heart rate and nausea, usually starting within hours and peaking over the next days. Severe withdrawal can bring seizures, hallucinations and delirium tremens, with confusion, fever and autonomic instability. Moderate and severe cases are treated with close monitoring and sedatives; benzodiazepines such as diazepam, lorazepam and chlordiazepoxide are the usual choice.
Thiamine and Wernicke–Korsakoff
Lack of vitamin B1 (thiamine) is common in heavy drinkers and in people who absorb food poorly. Wernicke's encephalopathy causes confusion, ataxia and abnormal eye movements; Korsakoff syndrome adds severe memory loss and confabulation. Thiamine given early often improves the confusion and eye signs, but the memory loss usually remains.
Methanol and ethylene glycol
Methanol is found in windscreen washer fluid, solvents, fuel additives and illicit or adulterated alcohol; ethylene glycol mainly in antifreeze. Both are converted by alcohol dehydrogenase into toxic acids. Methanol gives blurred vision or blindness, abdominal pain and coma; ethylene glycol gives metabolic acidosis and kidney failure with calcium oxalate crystals. Blood tests show a high anion gap acidosis and, early on, a raised osmolar gap. Outbreaks from contaminated drinks occur worldwide.
Treatment of toxic alcohols
Fomepizole competitively blocks alcohol dehydrogenase so the parent alcohol is excreted or dialysed before it turns into acid; ethanol works on the same enzyme and was the older antidote. Haemodialysis removes the alcohol and its metabolites and corrects acidosis, and is often needed. Fomepizole and ethanol slow each other's elimination, which matters when both are used.
Treating alcohol use disorder
Medicines support, but do not replace, psychosocial care: naltrexone reduces craving and reward, acamprosate helps maintain abstinence, and disulfiram makes drinking unpleasant by blocking acetaldehyde breakdown. Treatment coverage is very low worldwide.
Test yourself
Think of the answer, then tap the question to see it.
Why is thiamine given to a confused, malnourished patient with heavy alcohol use?
To prevent or treat Wernicke's encephalopathy, caused by thiamine (vitamin B1) deficiency.
Which metabolite causes the eye damage in methanol poisoning?
Formic acid (formate), made from methanol via alcohol dehydrogenase.
How does fomepizole work in ethylene glycol poisoning?
It blocks alcohol dehydrogenase, so glycolate and oxalate are not formed while the parent compound is removed.
Which drug group is the basis of treating severe alcohol withdrawal?
Sedatives, usually benzodiazepines (for example diazepam, lorazepam or chlordiazepoxide), with close monitoring.
Example drugs
Connections
Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.
Sources: Alcohol (World Health Organization, 2026); Alcohol withdrawal: MedlinePlus Medical Encyclopedia (MedlinePlus (U.S. National Library of Medicine), 2026); Wernicke-Korsakoff syndrome: MedlinePlus Medical Encyclopedia (MedlinePlus (U.S. National Library of Medicine), 2026); Methanol poisoning: MedlinePlus Medical Encyclopedia (MedlinePlus (U.S. National Library of Medicine), 2026); DailyMed - FOMEPIZOLE injection, solution (DailyMed (U.S. National Library of Medicine), 2026).
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