A fatal batch of synthetic cannabis is believed to have contributed to the death of a teen in the Hunter Valley.

Two others have also become critically ill in a neighbouring suburb.

Popular teen Dean Shield’s death was initially considered an accident, after he was found unresponsive in a drain on Saturday night.

View photos Dean Shield was tragically found in a drain on Saturday. More

His tragic death has since sparked a major investigation as detectives worked to determine whether the teen was experimenting with a form of synthetic cannabis.

Dean’s body was found by a Rutherford resident, hours after he was believed to have bought and taken the controversial substance.

Police are still trying to source the origin of the drug, after two more youths aged 22, fell ill.

View photos

Their conditions were not life-threatening.

Police have warned others who possess the drug to ‘throw it away’.

View photos Police have warned others with the drug to 'throw it away'. More

"Anyone using any form of drugs is putting themselves at extreme peril," Detective Inspector Dubojski told Fairfax.

The cause of Dean’s death will not be known until an autopsy is done, although toxicology could take much longer.

Police fear the ingesting of some form of synthetic cannabis lead directly to his death.

Brands of synthetic cannabis were outlawed in NSW in 2013 following a series of deaths, including two in the Hunter region.

Despite this, there have been concerns manufacturers have sidestepped the legislation by changing the drug’s chemical compounds so they varied from those banned.

It’s believed more popular drugs such as Chronic were being sold on the black market.

Dean’s sister Kayla Gynn told the Newcastle Herald her brother was ‘a good kid who could do anything when he put his mind to it’.

‘Honestly, there was never a dull moment when he was around,’ she said.