For me it was when I was alcoholic and developed a VERY severe case of a cute pancreatitis. I was in agony so they injected me with 10mg morphine every 4 hours for the ten weeks I was there. Because my alcohol withdrawal was so severe, the usual 50mg Chlordiazapoxide just wasn't enough so they added 2.5mg Lorazepam to it. And for some reason 1.5mg Haloperidol.
So I went from ZERO med/drug experience - apart from my prescription Sertraline to all this. By the time I left I was on:
(this is daily)
60mg IV Morphine (this is the equivalent of 180mg of oral Morphine)
300mg Chlordiazapoxide
20mg Lorazepam
4.5mg Haloperidol
And that's how I first experienced drugs and started my love affair with prescription medication.