Star Trek: Destruction by Alcohol

Alcohol and its effects on humans are well explored in the episode "The Naked Time", and how. A drunk Irishman from the Enterprise crew turns off the ships engine as its orbiting a collapsing planet and thats when the fun begins. The episode contains gems such as, a shirtless Sulu wandering the hallways with a sword, Scotty saying "I cannot change the laws of physics", traveling backwards in time and other geeky astrophysics fun. And best of all? Discovering the formula to travel back in time, how exciting.

Star Trek: The Original Series / The Naked Time

Star Trek: Posession

Star Trek: The Original Series was excellent for taking on fringe questions like race, greek gods and in the case of Episode "Operation Annhilate", posessions. The episode explores the parasitic mechanism, effect on hosts (physical & psychological-behavorial), complexity of curing and means of working around it. Must watch!

Star Trek: The Original Series / Operation Annihilate

I will let you watch the episode and conclude how close the writers come to the "cure" for posessions in this story. Its fun to watch how Spock shows his failing resistence to the parasite posession with twitches. Credits to writer