Yes, DIAZEPAMS is a Scrabble word!

Letter values in Scrabble US: D 2, I 1, A 1, Z 10, E 1, P 3, A 1, M 3, S 1.

Is it a valid word?

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

a tranquilizer (trade name Valium) used to relieve anxiety and relax muscles; acts by enhancing the inhibitory actions of the neurotransmitter GABA; can also be used as an anticonvulsant drug in cases of nerve agent poisoning

Not playable in Scrabble US: VALIUM.