Dr. Drew is weighing in on the NYC gunman who massacred 4 people with an AR-style rifle inside a Park Avenue skyscraper — and the famous doc is comparing the killer to the infamous Jeffrey Dahmer.

TMZ caught up with Drew over Zoom Tuesday after Shane Tamura went on his Monday night rampage inside the Midtown Manhattan tower before fatally shooting himself in the chest on the 33rd floor … after failing to reach the targeted NFL offices.

Police sources say Tamura left a 3-page suicide note saying he had a grievance with the NFL and claiming he suffered from CTE (chronic traumatic encephalopathy). As a result, he said he wanted his brain to be studied.

But, Dr. Drew tells us other doctors shouldn’t waste their precious time scanning Tamura’s brain for one reason — in the video clip, he says the scan won’t reveal anything about Tamura’s motive for killing all those people! Drew also says doctors don’t need to save the brain because “you need living brains to derive conclusions.”

At best, Drew says a scan would only confirm Tamura suffered from a neurological issue associated with a psychiatric illness — which could also include CTE.

Then Dr. Drew compared Tamura’s brain to Dahmer’s, pointing out the same would hold true for the Milwaukee serial killer, who snuffed out the lives of 17 men and boys from 1978 to 1991. In 1994, Dahmer was bludgeoned to death by a fellow inmate, while serving a life sentence in prison.

You may recall … Dahmer’s mother wanted his brain studied to see if there were biological factors that contributed to his lust for murder, necrophilia and cannibalism — but Dr. Drew says Dahmer’s case is the same as Tamura’s and doesn’t warrant further examination.

Still, an examination wouldn’t be in the cards anyway. A judge ordered Dahmer’s brain to be cremated in December 1995 during a legal battle between Dahmer’s divorced parents. Dahmer’s mother fought to preserve his brain, whereas Dahmer’s dad wanted to destroy it — and his father won.