(CBS News) -- The National Rifle Association's incoming president has linked school shootings and other violence to the use of medications such as Ritalin, but a medical expert who's studied the drugs says there's "no evidence whatsoever" of a connection.
Retired Lt. Col. Oliver North told "Fox News Sunday" that perpetrators of school violence "have been drugged in many cases" and "many of these young boys have been on Ritalin since they were in kindergarten." He also blamed a "culture where violence is commonplace," pointing to TV and movies.
North's comments followed the attack Friday at Santa Fe High School outside Houston that left eight students and two teachers dead. Investigators have given no indication that they believe the 17-year-old suspect, Dimitrios Pagourtzis, used Ritalin, which treats attention deficit hyperactivity disorder, or other drugs.
Pagourtzis' attorney, Nicholas Poehl, said Sunday that he was not aware that his client was on any specific medication. He said he was surprised that someone with North's experience with the criminal justice system would "make those kind of generalizations with a case that's less than 48 hours old."
An NRA spokesman, Andrew Arulanandam, confirmed North was speaking on the organization's behalf and said "there are others who share this viewpoint."
George DuPaul, a psychologist at Lehigh University in Pennsylvania whose research has focused on ADHD treatment, said a deeper body of research exists on the effects of Ritalin and similar drugs than of treatments for any other condition in children. He said it doesn't support North's claim.
"There's really no evidence whatsoever that links treatment for ADHD with Ritalin and drugs like that with violence, let alone gun violence," he said.
If anything, DuPaul said, children tend to be less aggressive.
"Certainly, there is some concern in the scientific and clinical community about the potential overreliance on these drugs," he said, "but it's a real stretch to go from that concern to connecting these kinds of drugs to these kinds of acts."
The FDA's medication guide on Ritalin says to watch for "new or worse aggressive behavior or hostility."
DuPaul said the warning may be a case of being "overly inclusive" of possible side effects or a hint to underlying issues in patients.
"What's more likely is that kids with mental health conditions who engage in this type of violent behavior, it's the underlying condition and not the treatment that leads to this behavior," he said.
The motive for the shooting is still under investigation. Social media posts from the suspect's accounts before the shooting included pictures of weapons and a T-shirt with the message, "Born to kill."
"This is a young kid who, at this point, is very confused and I think still in some shock," Pagourtzis' defense attorney said in an interview on "CBS This Morning" Monday.
Survivors of the shooting said the gunman roved back and forth between four classrooms, taunting students as he fired at them. A school resource officer who confronted the suspect was among those wounded. Pagourtzis surrendered to officers about half an hour later.
