How many people take psychoactive medication or similar because of some problems they have? How many of those people will, after x number of days without that medication, will become dangerous?

Mr. Red, again I have to agree here with Malgus,Huge number of folks are taking that kind of medication, big number of patients who are taking those kinds of drugs belong to the :
a) people who are gonna be pretty good without those drugs, with some good support of their family and friends (and maybe some alternative help, herbs for example)
b) people who are gonna be not so capable to accept (new) hard reality without those drugs, but they mostly not gonna be violent, they are not gonna be efficient, most probably they gonna be victims.

Of course there is a group of people, with some serious problems, who are “gonna lost it” without meds, small group, but yes they gonna be really violent.

Depends from the region of the world and laws about drugs I guess, and type of the SHTF. Here is not some problem to stock those type of drugs in bigger amounts, but yes when SHTF, sooner or later…
I remember that people with serious problems in some regions here were simply abandoned, yes there were psychos, seriously sick and dangerous people on street.