Mickey was drugged as the series progressed
We all know Mickey started off as a mischievous little mouse who tormented animals to make music and would smoke and drink in his early cartoons. He was also a player with Minnie and would often make advances on her. By the middle of the 1930s, the Disney Studio drugged Mickey when he needed to make cartoons so that he could be well behaved after all sorts of complaints were made against his behavior. This explains why Mickey is always so cheerful. It's the side effect of the drugs. By the early 1950s, Mickey had to get treatment for heavy drug usage which is why he didn't star in any cartoons until 1983
