As soon as anyone uses the excuse that a person behaved a certain way because they were under the influence of pharmaceuticals, there are immediately shushed by the general public. But this is dangerous. The fact of the matter is that these drugs to have a powerful effect that differs from person to person.
People with psychological disorders often seek out professional help for their issues. What they are given is a variety of highly questionable medicines designed to change their behavioral patterns. Sometimes medication works, other times it has an adverse or negative effect. If the shooter was on antidepressents it is certainly possible his disease was enhanced.
I think that the medications he was on were to held him for his psychiatric disorders but medications alone are not enough for some people, I think that there were likely many factors that went into Ivan Lopez's shooting rampage and investigators will slowly discover them as the investigation into this begins.
In order to help this gentleman he needed more than Pharmaceuticals, he needed constant supervision, he was really going through mental issues, just as anyone that needs counseling, this is nothing that can be healed over night, he needed some one to watch him and how he would sleep, talk, walk and all, all of these soldiers need to be supervised at all times, when they first come home from war.