Why do people take (illegal, deadly) drugs?

I am watching a documentary Airport Security and a drug was found in one case. It was illegal and it destroys the health, brain and the whole body. Why do people take drugs that destroy their body?

There are drugs that are deadly and it is well no secret.

I am asking about 1. time up to the 1. or 2. week and not longtime consumption.
Why do people take (illegal, deadly) drugs?
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