Miles Davis was one of the inventors of cool jazz. His early recordings are absolutely wonderful. But he wasn't the kind of artist you could nail down and his style changed throughout his life. Just like his heroin use.
He was addicted to heroin during the period that he did what is generally considered his best work in cool jazz. After that, he kicked. According to him, he went to his father's farm and kicked cold turkey. There is speculation that he chipped after that, even during the last years of his life. This is not well documented.