The phrase "I'm not a doctor, but I play one on TV" became popular in the 1980s thanks to the Vicks Formula 44 cough syrup commercials starring daytime soap opera actors Chris Robinson (GENERAL HOSPITAL) and Peter Bergman (then ALL MY CHILDREN, now THE YOUNG AND THE RESTLESS). Robinson's commercial ran in 1984 and it was duplicated almost exactly by Bergman in 1986. Below are clips from both:
Starts at 4:41