Picasso was quite into heavy drugs early on, morphine and opium for instance. But he quit also, before he turned 30 All his life alcohol was part of his diet, but not to the point of drowning into it So all in all, I don't think that's the main reason why his style "deperished" over time, rather a symptom of something else; self destruction, he was sort of into it, he had a difficult relationship with his father, who thought him how to paint... So, maybe that's not really painting he was "destructuring" in the end... But his relationship to his father, and it showed in what they shared in common, painting