Researchers found kids under six experienced plummeting blood pressure, dangerously slow heart rates, seizures, unresponsiveness and respiratory failure after only 1.7mg of THC per 2.2lb (1kg) of body weight – regardless of age or gender.

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A typical cannabis gummy contains around 10mg of THC – the psychoactive component that causes a ‘high’.

It means a toddler weighing 1st11lb (11.3kg) would exceed that threshold after consuming just two.

But scientists at Children’s Hospital Colorado Network discovered a single bite was enough to cause drowsiness, confusion, poor balance and coordination and vomiting.

Sometimes the effects lasted a couple of hours, while in others, symptoms persisted for more than 24.

Co-author Dr Lesley Pepin, a medical toxicology fellow at Rocky Mountain Poison and Drug Safety in Denver, said: “With widespread cannabis legalisation, we’ve seen a rise in unintentional cannabis exposures in children.

“In young children, these exposures are largely attributed to edible cannabis products (such as brownies, chocolate and gummies).

“Children sick from cannabis require hospital evaluation, medical observation and often need treatments such as supplemental oxygen or IV fluids.

“The effects can last hours or sometimes beyond a full day.”

The team looked at medical records from January 2015 to October 2022.

During this time, there were 80 accidental ingestion cases in children aged six and under that met the criteria for “harmful exposure” across four paediatric hospitals and urgent care centres.

The average age of patients was just under three, and 90 per cent of youngsters ate the gummies at home.

Analysis revealed the toxicity threshold to be 1.7mg of THC per 2.2lb (1kg) of body weight.

A total of 72 kids displayed symptoms within one hour, with sedation, lethargy and vomiting the most common.

While 34 required no further medical intervention after 1mg of THC or less per pound of body weight, 37 who consumed an average of 5.5mg per pound of body weight required immediate assistance.

Their side effects, which included seizures and comas and lasted 20.3 hours on average, meant some needed to be hooked up to ventilators and given blood pressure medication.

The researchers noted these cases were rare, and other factors may have contributed to individual impacts.

Eight kids displayed no symptoms at all.

‘SIGNIFICANT TOXICITY’

The authors said in the journal Paediatrics: “Ingestion of edible cannabis in children under six years old can lead to clinically significant toxicity.

“Based on our findings, a 10mg THC ingestion would be unlikely to cause severe toxicity in most young children.

“[However], with each additional 1mg/kg of THC, the odds of severe or prolonged symptoms triple.”

THC gummies are illegal in the UK as cannabis is a Class B drug.

However, because they don’t smell or look like weed, they are widely sold and often appeal to children, with brightly-coloured packaging and cartoon characters.

In the US, marijuana edibles are legal for recreational and medicinal use in more than 20 states.

Dr Tucker Woods, chair of the emergency department and associate medical director of Lenox Health Greenwich Village in New York City, said: “We are seeing more cases of this, and I expect to see even more now that marijuana is becoming legal in more and more states.

“These gummies are made for adults who weigh 120 to 160lbs on average, so for a kid who weighs 28lbs, one gummy could be enough to cause a coma or seizure.

“The less a child weighs, the greater the risk for ingesting a toxic dose of THC.”

While Detective Sergeant Karen Osborne, from Essex Police, previously said: “We want people to be aware of the dangers of taking cannabis edibles.

“Their consequences to young people – and indeed wider society – cannot be underestimated.

“The products may look harmless, and indeed ‘fun’, but they are very dangerous.

“Their effects are much-delayed, meaning young people are very likely to eat a dangerous amount before they even feel their effects.”

Experts recommend storing cannabis products in lockable cupboards that children can’t reach.

If you think your child has ingested marijuana, you should urgently seek medical help.