If you're part of my generation, you'll likely have a certain association with the words "Jesse Spano" and "caffeine pills." Yes, I'm sure the Pointer Sisters haven't sounded the same to you since.
Anyway, I don't envy writers stuck with an assignment to impart a message or life lesson to their audience. I think that it's possible to use drama and comedy to put forth certain messages or ideas. The problem is that when the message is the raison d'etre for the entire story, writers tend not to trust an audience to get any subtlety or nuance. Thus, the result is the "Very Special Episode." Sitcoms of the 80s and early 90s were crawling with these. For one week, the escapism you got from your favorite show would be replaced with the future Chandler Bing dying in a car crash to teach us all a lesson about drunk driving, or Alex Keaton having an emotional breakdown from survivor's guilt.
But those are only scratching the tip of the iceberg. Check out this salute to the Very Special Episode.