Four upstate New York children who were poisoned and killed by their mother and grandmother had an allergy medication that induces drowsiness and kratom in their systems, according to a new report.

The disturbing details into the horrific June murder-suicide in Mechanicsville were revealed in a toxicology report, sources told NewsChannel 13.

Harper Harmon, 13, and his three younger siblings — Hudson, 11; Gracelynn, 10; and Gavin, 10 — were all given kratom and diphenhydramine, the ingredient in Benadryl, before they died, according to the report.

Kratom — also known as “gas station heroin” — is a psychoactive herbal extract that can produce opioid-like effects, according to the Food and Drug Administration.

The four children were were allegedly killed by their mother Sarah Myers, 44, and their grandmother Amy Steadman, 64, who then took their own lives, authorities said.

Harper, Hudson and Gracelynn all died after they were poisoned, while Gavin was knifed while trying to defend himself, authorities said. 

Myers had been locked in a bitter custody battle with her ex-husband Brady Harmon, who lives in Utah and hadn’t seen his children in person since November 2019. 

The children were murdered shortly before they were expexted to spend the summer with their father in the Beehive State.

In a sick letter discovered by authorities after the slayings, Myers alleged that Harom had abused her and her children, and that the killings were the only way to save them from further abuse. 

Harmon denied the claims of abuse, and said there’s “a special place in hell” for his ex-wife. 

“My kids suffered,” Harmon told a local station. “To poison them and also to stab them – there’s a special place in hell for people like that.”