Green’s Dictionary of Slang

up adj.

[up adv.]

1. of drugs, extremely intoxicating or uplifting.

[US]R. Sabbag Snowblind (1978) 186: Rubia de la costa, the blonde from the coast, the finest, complete dynamite ‘up’ grass in the world. Take a hit.

2. stimulating, uplifting, high-energy.

[US]New Yorker 5 Aug. 21: It’s too down. I don’t like down movies. I like up movies.
[UK]Guardian Guide 19–25 June 11: It’s a very up show.