One of the world's only experts on the drug 25i testified Tuesday that 17-year-old Gavin Adams was likely profoundly impaired from taking the drug on the night he went missing in 2013.

Dr. Joji Suzuki was testifying in the Court of Queen's Bench trial of Richard Valiquette, 28, who is charged with criminal negligence causing death in connection with the death of the Saint John High School student.

Valiquette is accused of giving Gavin a substance not intended for human consumption and with reckless disregard for the teenager's safety.

Suzuki is the director of the addiction psychiatry division at the Brigham and Women's Hospital in Boston. He is considered an expert on 25i, the drug allegedly involved in Gavin's December 2013 death.

Image | Richard Valiquette

Caption: Richard Valiquette, 28, leaves the Court of Queen's Bench, where he is being tried on charges related to the 2013 death of Saint John teenager Gavin Adams. (CBC News)

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Valiquette's girlfriend in December 2013 earlier testified Gavin and a friend were stumbling like they were drunk and had difficulty opening the door when they left Valiquette's home on Dec. 14, 2013, the night Gavin went missing. Two days later, Gavin's frozen body was found half-buried in snow in a parking lot.

Suzuki testified symptoms of 25i use take 20 minutes to an hour to manifest and Gavin's described behaviour that night showed he had difficulty engaging in goal-oriented behaviour.

Suzuki testified 25i likely impaired Gavin's judgment profoundly as well as his ability to summon help or shelter. The drug may also have incapacitated him, Suzuki said.

Adverse reactions are more common with 25i than with classic hallucinogenic drugs, said Suzuki. Seizures, delirium and death can result, he said.

In two cases where 25i users died, bruises were found all over their body.

Many adverse reactions required extensive hospitalization in acute care, with users experiencing agitated delirium or renal failure.

Suzuki has co-authored numerous studies on drug abuse, including one dealing specifically with toxicities associated with a new class of synthetic hallucinogens called NBOMe.

The Court of Queen's Bench heard earlier this week that 25i, which belongs to the NBOMe class of drugs, was not a controlled substance in Canada at the time Gavin died.

Last week, amendments introduced in April to Canada's Controlled Drugs and Substances Act took effect, making the chemical a Schedule 3 substance.

On Oct. 3, Valiquette pleaded guilty to producing DMT.

Two other charges against him — drug trafficking and possession of a drug for the purposes of trafficking — were dropped.