How soon after trying does Heroin become addictive?

Addictive behaviour is one of those things that doesn't have a sharp turning point, at least in most cases. That's what makes it insidious - you're talking about a potential situation where your mind is fooling you into thinking you're in charge, when really you're diminishing your free will by steps. You're not necessarily going to be able to say when you lost control.

Some people try opiates, throw up and get constipated, and never want to see them again. I've know others who get them in hospital and are grateful for the pain relief but hate the side effects (some of which are probably the sought-after effects for someone who's become dependent). Some people maintain heroin addictions for years before kicking them, at a personal cost that's no less high for not being lethal.

Some things are very difficult to predict, and that's what makes them dangerous. If you've tried heroin once or a few times and find it pretty cool so far, you're probably on a slippery slope. If you haven't tried it, think about what you'd be trying to achieve if you did.

Uppers and downers generally don't lead to good outcomes, and heroin is very much a central nervous system depressant - like alcohol or barbiturates but more powerful. Powerful drugs are costly and the costs are hard to see beforehand.