Yes, CATNIP is a Scrabble word!

Letter values in Scrabble US: C 3, A 1, T 1, N 1, I 1, P 3.

Is it a valid word?

CATNIP is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

hairy aromatic perennial herb having whorls of small white purple-spotted flowers in a terminal spike; used in the past as a domestic remedy; strongly attractive to cats

Also: nepeta cataria.