Like all other physical things...
...drugs are a tool.
Used properly, with a concrete goal in mind, under proper guidance, they can be a tool for enlightement and transformation.
Used as most people today use them, without any guidance or help, without concrete goals in mind other than the annihilation of self-awareness in an attempt to escape the "Crazy Time" of our modern world, they lead to exactly what you have seen.
"He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you." - Friedrich Nietzsche