Why is meth so dangerous?

Addiction: It is highly addicting and chronic use has many bad health outcomes.

Unpredictable: The single most dangerous feature is that at any time -- the first or the 100th use -- you may suddenly discover you can no longer be happy without using it. You will continue compulsively and not stop until the adverse effects of the drug have killed you. The last stages are quite horrible. The stories about people ripping off their own flesh are true.