Methanol poisoning: symptoms, treatment and what to do

UKHSA says acute methanol toxicity often follows a characteristic series of features. Initially there may be central nervous system depression and gut irritation. This is typically followed by a latent period of 12 to 24 hours, occasionally up to 48 hours, in which the person may feel better. Subsequently a severe metabolic acidosis develops with nausea, vomiting and headache. Eye toxicity ranges from sensitivity to light and misty or blurred vision to markedly reduced vision and complete blindness. Coma and death may occur after substantial exposures.

Travel Aware presents the same pattern in plain language. It notes that spotting methanol poisoning can be difficult because at first it affects you in the same way as real alcohol, and warns travellers to watch for a hangover that feels worse than it should.

Methanol is an industrial alcohol made from distilling wood and found in products such as antifreeze, fuel and paint thinners. Travel Aware explains that in some parts of the world methanol products are sometimes illegally mixed with real alcohol such as spirit-based drinks and cocktails.

UKHSA's toxicological overview describes how it is the break-down products, rather than methanol itself, that cause the harm. In humans and primates, formic acid is considered to be the key toxicant, leading to a profound metabolic acidosis and damage to nerve cells, including those of the eye.

Travel Aware says that if you or someone you are travelling with has any of these symptoms after drinking, you should seek urgent medical attention. Get medical help straight away, do not wait to see if it gets better or go to bed and try to sleep it off, and call for emergency help or go to the nearest hospital. Emergency numbers differ by country and are listed in the health section of each country's travel advice.

In the UK, the NHS says to call 999 or go to A&E if you think you or someone else may have swallowed, touched or breathed in something harmful, or if someone has lost consciousness, stopped breathing, has severe difficulty breathing or has a seizure. Do not drive to A&E; ask someone to drive you or call 999. Call NHS 111 if you are not sure whether something is harmful.

While waiting for help, the NHS says to start CPR if someone is unresponsive and not breathing, put an unconscious person who is still breathing in the recovery position, try to find what caused the poisoning, and take some of the substance or its packaging to show doctors. Do not try to make someone sick and do not give them anything to eat or drink.

If you return to the UK and have been unwell after drinking abroad, mention possible methanol exposure to the doctor or NHS 111 adviser, because symptoms may not obviously point to it.

Travel Aware says doctors will give an antidote such as ethanol or a drug called fomepizole to stop methanol from turning toxic in the body, and may use dialysis to remove methanol and its toxic by-product. It stresses that treatment is most effective within 10 to 30 hours of drinking methanol.

UKHSA's overview explains the logic: alcohol dehydrogenase has a much greater affinity for ethanol than for methanol, which is why ethanol can block the production of toxic metabolites, and that aggressive alkaline therapy is required to keep formic acid in the form that does not cross into the brain.

The two can look alike at first, which is one reason methanol poisoning is hard to spot. The NHS describes alcohol poisoning as happening when you drink alcohol quicker than your body can process it, with confusion, slurred speech, poor coordination, vomiting, slow or irregular breathing, seizures or loss of consciousness. Travel Aware says early methanol signs can resemble this, but a hangover that feels worse than it should, or any problem with vision, is a warning sign.

UKHSA says long-term effects may include blindness and, following more substantial exposures, permanent damage to the central nervous system, which can show as a Parkinson-like condition. Ingestion of as little as 4 to 10mL in adults may cause permanent damage according to the same overview, and the minimal lethal dose is estimated to be in the range of 300 to 1,000mg per kg.

Survivors can face vision loss, movement problems and psychological effects. One survivor quoted by Travel Aware describes anxiety out of proportion to situations and difficulty travelling after her experience, which illustrates why support after poisoning matters.

Travel Aware says it is not possible to remove the risk completely but travellers can take steps. Avoid free cocktails or shots, unlabelled bottles and unusually cheap or discounted drinks claiming to be brand name alcohol, and be careful with spirit-based drinks such as shots, cocktails, buckets or jugs. Choose branded beers, ciders, wines and premixed cocktails in sealed bottles and cans, buy from licensed stores, bars, clubs, restaurants and hotels, and avoid homemade, bootleg or street-side alcohol.

Keep an eye on your drink, and check the FCDO travel advice for your destination before you travel. It is sensible to learn the symptoms before you go and to agree with friends that nobody sleeps off a hangover that seems unusual.

UKHSA says methanol may be acutely toxic following inhalation, oral or dermal exposure, and that long-term inhalation of low concentrations has resulted in headaches and eye irritation in workers. It is not classified as a mutagen or carcinogen in humans, and it is not classified as a human reproductive toxicant. Travel Aware lists antifreeze, fuel and paint thinners among the commercial products in which methanol is found, so swallowing any of these is a poisoning emergency, not a drinking problem.

Suspected methanol poisoning is an emergency handled through 999 and hospital emergency departments, where treatment includes antidotes and sometimes dialysis, according to Travel Aware and the NHS poisoning page. It is not something to book as a routine or private appointment. If you are abroad, use local emergency services first and keep your travel insurance details to hand, because costs and repatriation arrangements vary.