KITCHENER - Over-the-counter eye drops are safe products when they're used as intended, but can have dangerous consequences when abused as a prank or something more malicious, says the director of the pharmacy school at the University of Waterloo.

"There's unfortunately been some high-profile examples of people using eye drops orally to get back at people they don't like," David Edwards said. "To the best of my knowledge, no one has ever died from this type of poisoning, but there are very serious side-effects."

Those side-effects can include abnormal drowsiness, sedation, low or high blood pressure, difficulty breathing, decreased heart rates and even a coma.

Tetrahydrozoline is the active ingredient - made up of carbon, hydrogen and nitrogen - that's found in eye drops and nasal decongestant sprays.

"Tetrahydrozoline constricts blood vessels and because of that, it stops your nose from running and clears up red eyes," said Edwards.

The most well-known product example is Visine, he added.

In the wake of the arrest Monday of a 32-year-old Kitchener woman charged with poisoning two young children in her care with tetrahydrozoline, attention has centred on the chemical.

But its use as a poison isn't new. An urban legend termed the "Visine prank" suggests that tetrahydrozoline causes violent diarrhea if taken orally, popularized in the 2005 comedy Wedding Crashers, where one of the main characters puts eye drops in a rival's drink.

The film scene is alleged to have inspired a number of copycat crimes. Five high school students in Milwaukee nearly killed a classmate by imitating the prank in June 2006. A Wisconsin woman was jailed for 90 days for repeatedly poisoning her roommate's water with Visine in 2011, confessing that she got the idea from the movie. In March 2013, a California man was charged with domestic violence and poisoning after he spiked his girlfriend's drink as a prank following an argument between the couple.

A Google search for "Visine prank" yields over 19,500 results, including several more cases of poison pranks, most occurring from 2005 onwards.

Although it's commonly believed that ingesting tetrahydrozoline will cause diarrhea, that's not actually the case, said Edwards.

"It's much more dangerous than people think," Edwards said. "These deliberate poisonings might not be designed to do dramatic damage, just to make someone feel terrible, but eye drops are obviously designed for topical use and I think any time you're taking something in a different way than it's intended, you've got potential problems."

Edwards doesn't think people should overreact, though. "Eye drops and nasal sprays are very, very safe products when used as intended," the pharmacy school director said, adding that most of the products are designed for adult use rather than for children and dosage instructions should be carefully followed.

The Record reached out to Johnson & Johnson, the company that produces Visine, for their thoughts on the abuses of the product, but they didn't provide comment.

Christine Allen, who operated an unlicensed home daycare in Kitchener between 2009 and 2011, was charged with two counts each of aggravated assault and administering a noxious substance. Waterloo Regional Police allege Allen used an over-the-counter eye care product containing tetrahydrozoline in two separate incidents. In both cases, two children under her care had to spend several days in hospital receiving treatment after ingesting the product.

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Police say anyone who left a child in Allen's care should speak to them. Speaking Tuesday, police spokesperson Olaf Heinzel said police have received tips from the public but would not comment on whether more parents have come forward with allegations of poisoning.

Police continue to investigate and are asking anyone with information to call detectives at 519-653-7700 ext. 4437 or Crime Stoppers at 1-800-222-8477.