An Oklahoma teenager has been left critically ill after trying a viral social media trend known as the "Benadryl challenge," which has left several children in hospital.

The challenge involves individuals taking excessive amounts of Benadryl and attempting to stay awake through the induced drowsiness to receive a high. It can cause serious side effects, including seizures and cardiac arrest.

Leah Presson, 15, is being treated in an intensive care unit in Oklahoma and multiple tests have shown that she has zero brain activity, according to the local news outlet KFOR.

The teenager's father, Richard Presson, told the outlet: "I don't even want to think about a funeral because I feel like there's still hope and everybody's like, giving up too soon... I believe in miracles, that she's definitely a miracle baby."

He added: "I just want everybody to be aware of where they can educate their kids. But these challenges are just silly, and they need to be educated so it doesn't happen again."

This is a developing story. More to follow.