Methanol poisoning can occur when contaminated alcoholic drinks are consumed. This is a global problem, with several hundred outbreaks affecting numerous people each year. In severe cases, methanol exposure can lead to blindness, respiratory issues and even death.

Poisoning events involving methanol are rarely out of the news. More than 160 people are reported to have died from methanol poisoning in Turkey at the start of this year with dozens more hospitalised. Another nine people died in Jordan in July following consumption of alcoholic drinks contaminated with methanol. In August, tainted alcohol killed 13 people in Kuwait, and blinded another 21. And last month, UK prime minister Keir Starmer was urged to raise the methanol poisoning deaths of two British citizens in Vietnam, Greta Otteson and Arno Quinton, with the country’s leader.

A lack of awareness of methanol poisoning’s symptoms can contribute to misdiagnosis and delayed treatment. However, a new sensor developed in Australia can detect methanol up to parts per billion and could potentially prevent numerous cases of methanol poisoning if simple devices like these can be rolled out to consumers.

But how is methanol ending up in alcoholic drinks in the first place?

What is methanol?

Methanol (CH₃OH) is the simplest alcohol. It is structurally similar to its more well known relative, ethanol (C₂H₅OH), which is the ingredient that gives alcoholic beverages their intoxicating effects.

Around 138 billion litres of methanol are produced each year and this is predominantly used as an industrial feedstock to synthesise other chemicals such as formaldehyde. Industry also uses methanol to produce antifreezes, perfumes, fuels and solvents.

So how does methanol end up in drinks?

Fermenting fruit or grain with yeast is the usual way of making alcoholic drinks, with alcoholic content reaching between 12–16% before fermentation efficiency decreases. Distillation can then raise the alcohol content by evaporating and condensing the alcohol, leaving behind excess water.

This distillation process is useful for removing any methanol that is produced as a side product of fermentation. Methanol has a lower boiling point (64°C) than ethanol (78°C), meaning distillation of methanol occurs first. Discarding the first few distillates, known as foreshots, removes methanol and unpleasant-tasting compounds from the final product. Poorly managed distillation, which usually occurs during small scale fermentation, can lead to the presence of unwanted methanol.

Unintentional methanol contamination is more likely to occur in traditionally fermented alcoholic beverages. Here, alcoholic drinks are made using fruits – such as grapes and berries – that are high in pectin, a naturally occurring sugar found in the cell wall of most plants. Certain yeasts, bacteria and fungi can metabolise pectin into pectic acid and methanol, thanks to the enzyme pectin esterase. Improper sterilisation of equipment or the deliberate use of wild yeast can introduce these esterase-producing microbes into the brewing process. Such fruits are frequently fermented to produce higher percentage alcohols, such as palm or plum wine, further increasing the risk of a higher methanol percentage.

Bootleg brewers also sometimes add enough methanol to informally produced spirits to cause serious health effects. In countries where the production and selling of alcoholic drinks is illegal, these brewers do this as a cheap way of raising the alcohol content.

What happens when you consume a drink containing methanol?

Despite methanol’s bad press, the compound itself is not intrinsically toxic. The metabolism of methanol is where the real issue lies.

Methanol is first oxidised by alcohol dehydrogenase to form formaldehyde. Aldehyde dehydrogenase further oxidises formaldehyde to create formic acid, the toxic chemical behind methanol poisoning. These enzymes are also responsible for metabolising ethanol, forming acetaldehyde and subsequently acetic acid. Alcohol dehydrogenase is 20 times more selective for ethanol than methanol, meaning in alcoholic drinks containing trace amounts of methanol, metabolism of methanol is limited. However, in drinks that contain more methanol, the ethanol is metabolised quickly, which then allows for methanol metabolism to occur, generating formic acid. This formic acid can be removed from the body by being broken down into carbon dioxide in a pathway involving folate, though this process is slow, allowing formic acid to build-up.

An excess of formic acid lowers blood pH and inhibits mitochondrial enzymes. Methanol poisoning can lead to blindness in severe cases, as retinal cells are rich in mitochondria as constant conversion of photons into electrical signals is an energy-intensive process. This means that the retina is particularly sensitive to high levels of formic acid, with as little as 4ml of ingested methanol leading to permanent eye damage. Formic acid also severely depresses the central nervous system, which can lead to hyperventilation and cardiac arrest, resulting in death.

A normal blood methanol concentration is less than 0.5mg/l. The World Health Organization associates levels above 500mg/l with severe toxicity, whilst concentrations in the range of 1500–2000mg/l are fatal, if left untreated.

Can methanol poisoning be treated?

Poisoning is treatable if diagnosed within 10–30 hours. However, this is often difficult as ethanol and methanol produce similar initial symptoms, such as dizziness, nausea and lack of coordination. Later, more severe symptoms can develop due to methanol ingestion, such as abdominal pain, blurred vision or difficulty breathing. These symptoms may not show until as late as 48 hours after ingestion, making diagnosis difficult.

Administering patients with controlled doses of either ethanol or fomepizole is standard practice. These compounds are competitive inhibitors for alcohol dehydrogenase, reducing the amount of methanol converted into toxic formic acid. The kidneys can then slowly excrete the methanol from the body, with external dialysis often administered to aid and speed up this process. However, fomepizole’s current price rises as high as thousands of dollars per dose, making it too expensive for those in countries most affected, despite the World Health Organization listing fomepizole as an essential drug.

Other treatments include administering sodium bicarbonate to neutralise formic acid and correct pH levels of blood and other bodily fluids, and physical support for patients such as mechanical ventilation and intubation.

Where are you most likely to get methanol poisoning?

Methanol poisoning can be challenging to diagnose, with symptoms often disguised or delayed. This can hide the true number of poisonings around the world. Statistics from Medecins Sans Frontieres show that the issue is global and has affected over 40,000 people and killed 14,000 over the past 25 years. However, Iran, India and Indonesia make up half of all recorded cases. In 2023, fomepizole was used in 3000 cases of methanol poisoning in the US, according to the United States Poison Centre.

Last month, the UK’s Foreign Office added methanol poisoning advice to the advisory information on eight countries, including Japan, Mexico and Nigeria, bringing the total number of countries with such warnings to 16.   

How can you reduce your risk of methanol poisoning?

The World Health Organization and the Foreign Office have listed some ways that individuals can protect themselves against methanol poisoning:

• Be wary of alcoholic drinks being sold in informal settings or at very low prices.
• Check that labelling is authentic, properly printed and that bottles have unbroken seals.
• Know the symptoms of methanol poisoning and seek medical attention as soon as possible.
• For those brewing their own alcoholic drinks, ensure that commercially available yeast is used and that equipment is thoroughly sterilised. This will prevent unwanted contamination with microorganisms that could lead to a higher methanol content.