The People Next Door (1970)

Comfortable New York suburbanites Arthur and Gerrie Mason discover one night that their seemingly perfect 16-year old daughter, Maxie has been tripping on LSD. Arthur, a smug, bullying braggart, immediately suspects his 17-year old (long-haired) son, Artie of supplying the drug to his sister, and immediately kicks him out of the house.

Whereupon (suitably) confused Harris runs next door to seek advice from high school principal David Hoffman whose wife, Tina is an alcoholic, and whose son Sandy has his own problems. Very sensibly, he advises love and understanding on the part of the parents, which all but goes out the window when Maxie confesses she has been tripping for quite a while now, is also sexually active and on the pill. Meanwhile, she just keeps getting worse she's found by her father high on cocaine and in bed with a biker. From there, it's straight to family therapy where, among other things, it's revealed that Dad is having an affair with his lusty secretary and Mom knew it all the time. After another lamentably useless therapy session, the Masons decide to throw a party which comes to an abrupt halt when one of the hired musicians is discovered puffing pot. Maxie then gets hold of more LSD, does a nude dance on her lawn and trips herself into a mental hospital. The sight of her near-catatonic daughter in this horrible place drives Mom right to bed, where she remains until the film's climax.