It's subjective. Addiction affects people on different levels and in different forms depending upon life experiences, environment, genetics, etc.
For example, alcoholism, some people are more genetically predisposed to becoming alcoholics than others, and with that, full blown alcoholism is a form of chemical dependancy of which treatment would involve medication and harm reduction, because once you're at that point you can't just up and quit because alcohol withdrawals can be fatal.
Opiates, depends on the quantity/potency. There's a difference between popping pills and shooting dope up. People can(and often do) become addicted to pills, but when you start, it's still up to your willpower to not do it on a reg basis where it becomes a habit, then addiction. Heroin on the other hand, you only gotta shoot that shyt up one time and you're addicted, like your body's on chemical dependancy level off jump. Either way once you're addicted to opiates, that's chemical dependancy that is usually treated by medication. Some of those medications turn into other addictions though.
Meth can also cause a chemical dependancy quickly. But about everything else would be pretty much be about will power. There's people who can sniff coke/smoke rocks while partying on the weekend and still keep a job. It depends on the individual. Everything has withdrawal symptoms, even weed and caffiene. Some are just barely there and don't last long while others can affect you for life physically and mentally
