I dont think its the same as suicide because you're not intentionally trying to die from an overdose. Sure people know that they can die from taking high doses of a drug, but people know they can have serious consequences from going to the beach and getting a tan without putting on suncreen too, like getting skin cancer, or eating way too much junk and having a heart attack. Plus, a lot of people who die from ODing were addicted to the drug, and unfortunately for whatever reason were unable to receive help before the problem got out of hand. So, no, if I believed in God and believed in heaven and hell, I wouldnt think people who ODed would go to hell.