Whatever drug he was on, if any, this much is certain: If just one sane teacher or sane student had been carrying a concealed weapon, the killer could have been shot long before he took so many lives and wounded so many others. Just one normal person with a weapon could have saved most of the others.
The psychiatrists don’t really know what will happen when they prescribe drugs. They are just guessing, playing with lives, and the consequences have often been fatal. Too often, the “cure” is worse than the mental imbalance.
Making the dangerous assumption that a prescription indicates that a doctor is actively monitoring the person, I find this to be very preferable to having someone self-medicate. The tower shooter in Austin, TX was a alcoholic, other school shooters have used other drugs.
The one part of the profile for school shooters that I am waiting to see come out, loner and depressed are already there, is the obsession with violent video games, movies, or songs, or possibly all listed.