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# Methanol poisoning

Methanol from adulterated liquor or industrial products turns into formic acid, which causes severe acidosis and blindness.

Updated 2026-11-01

## Structures involved

Tap one to see what it is and open it in 3D.

- [Optic nerve](https://durgical.com/en/anatomy/optic-nerve/)
- [Putamen](https://durgical.com/en/anatomy/putamen/)
- [Retina](https://durgical.com/en/anatomy/retina/)
- [Optic disc](https://durgical.com/en/anatomy/optic-disc/)

## In biochemistry

- [Ethanol metabolism: Step 1 · Alcohol dehydrogenase (ADH, class I)](https://durgical.com/en/biochemistry/pathways/ethanol-metabolism/#paso-1)
- [Alcohol dehydrogenase (ADH)](https://durgical.com/en/biochemistry/enzymes/alcohol-dehydrogenase/)
- [Ethanol](https://durgical.com/en/biochemistry/molecules/ethanol/)
- [Fomepizole (4-methylpyrazole)](https://durgical.com/en/biochemistry/molecules/fomepizole/)

## In physiology

- [Metabolic acidosis, the anion gap and compensation](https://durgical.com/en/physiology/metabolic-acidosis-the-anion-gap-and-compensation/)

## Why it happens

- [Chemical (toxic) cell injury: direct and after metabolism](https://durgical.com/en/general-pathology/chemical-cell-injury-direct-and-after-metabolism/)

## What it is

Poisoning by methyl alcohol, usually swallowed in adulterated drinks, which the [liver](https://durgical.com/en/anatomy/liver/) turns into formaldehyde and formic acid.

## Who gets it

It occurs in outbreaks from adulterated or bootleg liquor, with many victims at once; such outbreaks have been described in Colombia and other Latin American countries, plus isolated cases from industrial products or fuels.

## Causes

- Adulterated or poorly distilled home-made liquor
- Solvents, windscreen washer fluid, fuels and laboratory products
- Accidental ingestion in children or intentional ingestion

## Risk factors

- Drinking liquor of unknown origin or very cheap liquor
- Alcohol dependence
- Work with solvents

## Pathophysiology

Methanol itself is not very toxic. Alcohol dehydrogenase oxidises it to formaldehyde and aldehyde dehydrogenase to formic acid (formate). Formate inhibits cytochrome c oxidase (complex IV): the cell switches to anaerobic glycolysis and adds lactic acid. The result is a high anion gap metabolic acidosis; early on the osmolal gap is also high, falling as methanol is converted. The [retina](https://durgical.com/en/anatomy/retina/) and [optic nerve](https://durgical.com/en/anatomy/optic-nerve/), with high ATP demand, and the putamina suffer first. Formate is cleared slowly through a folate-dependent route. Ethanol drunk at the same time delays symptoms because it competes for the enzyme.

## Symptoms and signs

- At first, mild drunkenness or nothing
- After 12–24 hours: nausea, vomiting, abdominal pain and headache
- Blurred, «snowfield» vision, photophobia or blindness
- Fast, deep breathing (Kussmaul)
- Confusion, seizures or coma

## Red flags

- Any visual disturbance after drinking liquor of doubtful origin
- Several patients ill after drinking the same liquor
- Unexplained high anion gap metabolic acidosis
- Dilated, unreactive pupils

## Diagnosis

**Clinical**
History of ingestion with visual symptoms and acidosis after a symptom-free interval of hours; suspected even when no level is available.

**Tests**
Arterial blood gases and electrolytes (high anion gap acidosis), measured osmolality and osmolal gap, methanol and formate levels if available, lactate, [kidney](https://durgical.com/en/anatomy/kidney/) function, glucose and ethanol level.

**Imaging**
Head CT or MRI can show necrosis or haemorrhage of both putamina in severe cases; fundoscopy shows [optic disc](https://durgical.com/en/anatomy/optic-disc/) oedema.

## Treatment

**Acute**
Airway, breathing and circulation support in the emergency department; correction of acidosis with bicarbonate.

**Medical**
Antidote: fomepizole, or ethanol when fomepizole is unavailable, to block alcohol dehydrogenase.

**Medical**
Folinic acid or folic acid as an adjunct to speed formate clearance.

**Procedure**
Haemodialysis to remove methanol and formate when there is severe acidosis, visual damage or high levels.

**Follow-up**
Monitoring of blood gases, electrolytes, vision and neurological state; notification of public health when an outbreak is suspected.

## Drugs for this condition

- [Fomepizole](https://durgical.com/en/pharmacology/fomepizole/)

## Complications

- Permanent blindness from optic atrophy
- Putaminal injury with parkinsonism
- Acute kidney failure
- Death

## Prognosis

It depends on time to antidote and dialysis: very low pH, coma and seizures on arrival point to a poor outcome; visual sequelae are common.

## Prevention

- Control of liquor sales and industrial alcohol
- Avoiding unregistered liquor
- Labelling and safe storage of solvents

## Test yourself

Think of the answer, then tap the question to see it.

## Which methanol metabolite causes blindness and acidosis?

Formic acid (formate), which inhibits cytochrome c oxidase.

## Why do symptoms appear hours after ingestion?

Because methanol must first be converted to formaldehyde and formic acid; if ethanol was drunk too, it is delayed further.

## Which blood gas and osmolality pattern suggests methanol?

High anion gap metabolic acidosis and, early on, a high osmolal gap.

## Which brain structure is typically injured in severe methanol poisoning?

The putamina (bilateral necrosis), besides the optic nerve.

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## Related conditions

- [Ethylene glycol poisoning](https://durgical.com/en/conditions/ethylene-glycol-poisoning/)
- [Lactic acidosis](https://durgical.com/en/conditions/lactic-acidosis/)
- [Diabetic ketoacidosis](https://durgical.com/en/conditions/diabetic-ketoacidosis/)
- [Acute kidney injury](https://durgical.com/en/conditions/acute-kidney-injury/)
- [Cyanide poisoning](https://durgical.com/en/conditions/cyanide-poisoning/)
- [Carbon monoxide poisoning](https://durgical.com/en/conditions/carbon-monoxide-poisoning/)

Educational information, not medical advice. For any symptom, see a health professional.

Sources: [Methanol poisoning: MedlinePlus Medical Encyclopedia](https://medlineplus.gov/ency/article/002680.htm) (MedlinePlus, US National Library of Medicine, 2026); [Methanol (CID 887)](https://pubchem.ncbi.nlm.nih.gov/compound/887) (PubChem, NCBI, 2026); Textbook of Biochemistry for Medical Students, 6th ed. (Jaypee Brothers Medical Publishers (Vasudevan DM, Sreekumari S, Vaidyanathan K), 2011).

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Source: https://durgical.com/en/conditions/methanol-poisoning/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/conditions/methanol-poisoning/