https://www.researchgate.net/profile/Peter-Langman/publication/308220517_Psychiatric_Medications_and_School_Shootings/links/57dec49908aeea19593b4d96/Psychiatric-Medications-and-School-Shootings.pdf?origin=publication_detail
How many school shooters were on psychiatric medications — or coming off them — at the time of their attacks? The following data is drawn from the sample of 48 shooters profiled in my book School Shooters: Understanding High School, College, and Adult Perpetrators. Out of 24 secondary school shooters, only two were taking medication at the time of their attacks: Eric Harris and Jeffrey Weise. Alvaro Castillo might have been, or he may have stopped his medication within three weeks of his attack and thus still have been coming off the drug. If we include him, then 12.5% of the sample was taking medications. Put differently, over 87% of the secondary school shooters were not on psychiatric medications at the time of their attacks. Furthermore, there is no evidence that medication made Harris, Weise, or Castillo manic or psychotic.

The numbers are essentially the same for the college and adult shooters. Of the 24 in these two groups (13 college and 11 aberrant adult), two were taking psychiatric medications at the time of their attacks: Laurie Dann and Matti Saari. Because Steven Kazmierczak had only recently stopped taking his medication, perhaps he should be included, for a total of three shooters with at least some trace of medication in their bodies at the time of their attacks. Thus, 12.5% of the college and adult shooters were on medication at the time of their attacks. Again, there is no evidence that medication made them manic, agitated, or violent. Taken all together, only 6 out of 48 shooters (12.5%) were on medication at the time of their attacks. Even if we were to accept that psychiatric drugs caused these attacks, this still leaves over 87% of the incidents unaccounted for.