Yes, you are correct. My sister, a druggie, is one of them. But she is also bi-polar, has threatened to kill people, and is border-line schizoid.
So the question remains: do people use marijuana and opiates to self-medicate? Or does the decades-long use of these types of drugs cause a person to mentally degenerate?
Why wouldn't it? It's both behavoral and physical deficiencies catching up with them.