This is a TV movie about a high-school girl who has a problem with alcohol. It's not a bad example of the "after school special" genre, but it's mainly interesting because of the actors in it.
Mark Hamill plays the boyfriend of the main character. This was a couple years before Star Wars (and far, far away from the abominations that Disney would later produce).
Linda Blair plays the main character; she'd recently starred in The Exorcist, had been doing a number of supporting roles in films, and would go on to make a series of horror films.
Other actors of interest include Larry Hagman who had a number of other successful TV roles such as "I Dream of Jeannie" and "Dallas", and William Daniels who did the voice of KITT the talking car in Knight Rider.
Other than that, the "70s mood" abounds...
- The link from above: https://www.youtube.com/watch?v=EvcXvkJwORY It has Italian subtitles, but they're not embedded, you can turn them off.
- Look for an Invidious instance: https://redirect.invidious.io/watch?v=EvcXvkJwORY
- For more information see: https://en.wikipedia.org/wiki/Sarah_T._%E2%80%93_Portrait_of_a_Teenage_Alcoholic
edit: BONUS FILM: "Cocaine: One Man's Seduction" (1983 480p) - another TV movie, this time about the perils of powder cocaine. James Spader plays a supporting character in an early role.