What stretchysumo said is true. Media likes to say that you do substances once and get hooked, but really that's not how drugs, or the human body work. When drug users say,"I tried it, and I was hooked" what they really mean is, they tried it, it was amazing, and they wanted to do it ever since.
Cocaine, Meth, Heroin, all require consecutive uses to become physically dependent. I personally would never shoot up, nor suggest that anyone else should, but that's your choice to make bro.
The main reason why drug addicts overdose isn't necessarily from dependence.(tho it can be)
Bradley Nolls from Sublime, for example, has been labeled a heroin "addict." In actuality, he binged off and on, and it was never really an issue for him. It's when you stop for long periods of time, and start back up again that your body cannot handle it, and you can overdose.
Everybody's body is different, too, and some people can handle large amounts of heroin without overdosing. Others do a small amount, and have an adverse reaction to it. It just depends. Be cautious when trying anything new.