questions about consequences of drug abuse?

Hi, I’m doing a research on drug addiction and here are several questions i have in mind. please take your time in answering them. thank you.

1) When drug abusers who are highly addicted to illegal substances do an immediate stop (No rehabilitation or anything, they just completely stop the habit by themselves though their body still wants it), are there any chances of death? coma? or anything that could put you to sleep for a very long time. If so, then how long?

2) What are the symptoms of high level of drug abuse?

3) What are the chances for an average person to do a complete stop?

4) What are the stages of an immediate stop? Are there any?
“e.g.: shaking, compulsion, etc.”
what are the chances of a person dying or going into deep coma?
by being taken together, do you mean together at the same time? or together as in alternately taking them one after the other?

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