Lizzy, perhaps the ruling was made based on quantities and when he took the - I would guess it was determined that he didn't take them all at once. Many users combine drugs - it is common to take ativan and/or xanax and/or klonopin to come down from or smooth out a cocaine high. Oxycodone is for longterm pain relief and vicodin is for breakthrough pain - benadryl would potentiate either of those drugs and may have been taken for that reason.
Most users who OD don't mean to and are used to ingesting multiple substances. I know that doesn't sound sane to a non-user and that's because it's not sane. But it's not overtly suicidal for a user.
To give an example from my own life. These are the drugs they found in his system: cocaine, oxycodone, hydrocodone (Vicodin), Ativan, Klonopin, Xanax, Benadryl and Levamisole (a drug used to cut cocaine with). I can think of more than one occasion when I was using that I took, over the course of a day, cocaine, oxycodone, hydrocodone, Ativan, Xanax, Benadryl, marijuana and alcohol. But in no way was I trying to kill myself - I didn't even think what I was doing was all that risky based on my tolerance and experience.
