How do drug addicts die from poisoning?

2 reasons, the commonest is that the drug they buy has been 'cut' or diluted with potentially fatal additives. The second is that the drug is more potent than usual and they die effectively from respiratory depression due to the overdose.

Also, to much of a drug shuts down your posterior brain; responsible for respiration, and it doesn't remind itself to breath and death is the result.

The liver also fails from to much of a drug. And it poisons the body and brain. Global encephlopathy.

they start from a small dose and think they can contoll it then they increase the dose because they start to feel bad and need it more and more.This leads to an overdose which basically means there is too much chemicals in your blood system and your organs cant handle it and shut down

same as anyone else would. it isnt the actual drug that kills you its the amount of it you ingest. even paracetemol will kill you if you take too much.