Summary: This post advocates taking guns away from people who are under psychotropic medication.
Helsingin Sanomat published a long and sad article about Hyvinkää shooting case with 2 dead and many more injured for life. The outcome would have been much worse without a police squad shooting back minutes after the shooting started. Among other things the article tells that the shooter was under influence of fluoxetine, an SSRI antidepresant.
Out of 5 recent mass killings in Finland (Hyvinkää shooting, Kauhajoki shooting, Jokela shooting, Myyrmäki bombing, Sello shooting) in 60% of cases the shooter has been under SSRI medication. For the remaining 40% medication is not known from open newspaper articles.
This prompted Tapani Sipilä, an emeritus M.D. of psychiatry, to call for review on how much antidepressants are prescribed and to pay closer attention to their adverse side effects (2012) The medication is safe and beneficial for most people to whom it is prescribed, but for some subgroups it either doesn't work or causes aggression or anger as a side effect.
Also professsor Jari Tiihonen's research group studied if psychotropic drugs increase killings. The study had N=959 killers and ten times as many controls. They found that SSRI drugs only mildly increased risk of killing. The effect bordered between random noise and statistical signifigance. However, pain medication significantly increased risk of killing. Also 80% of killers were drunk while killing.
The study is a bit irrelevant for preventing mass shootings, since we can't wait for statistically significant number of mass shootings to happen. Even if SSRIs do not increase regular murdering, they might reduce the barrier for committing a mass shooting in some subgroup with special brain chemistry.
Taking guns temporarily away from people who are under antidepressants, regular pain medication or their withdrawal phase would have prevented 40% of Finnish mass shootings. In Hyvinkää shooter Eero Hiltunen's case this wouldn't have worked, since he didn't use a licensed gun. He started to saw through his father's gun closet until finding a key. SSRI use marks the risk group of mass shooters so well that it is irrelevant if SSRI antidepressants cause mass shootings or underlying mental problems cause both SSRI use and will to commit a mass shooting. It is enough to know that mass shootings can be prevented by taking guns away from people under SSRI medication.