ODs are experienced by drug users who want to chase their first high. Brain and organ damage isn't really an issue, either, as the drug is not often inherently toxic. It might have physical effects such as ruining your brain's dopamine systems, changing your skin (meth or lifetime needle user), rotting your teeth (smoking) and making your depressed, but very few drugs are actually dangerous when used in moderation.
It's like playing on a cliff: there might be one or two drawbacks like you being a bit cold, but other than that, it's loads of fun when you don't go too close to the edge. If you fall off the edge and get addicted, though, you're often to blame. The thing that differentiates different users is how often they go to play on the cliffside how grippy their shoes are and how close to the edge they play.