When someone drunks alcohol, it goes into their bloodstream where it affects the central nervous system (the brain and spinal cord), which controls virtually all body functions.
Vicodin overdose can occur both in individuals who have been legitimately prescribed the drug, and in individuals who abuse it illegally.
PCP users are commonly brought to emergency rooms because of overdose or because of the drug's severe psychological effects.
When someone injects heroin intravenously this is called mainlining.