Yes, CONSTITUTIONAL is a Scrabble word!

Letter values in Scrabble US: C 3, O 1, N 1, S 1, T 1, I 1, T 1, U 1, T 1, I 1, O 1, N 1, A 1, L 1.

Is it a valid word?

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

of benefit to or intended to benefit your physical makeup
sanctioned by or consistent with or operating under the law determining the fundamental political principles of a government
existing as an essential constituent or characteristic
constitutional in the structure of something (especially your physical makeup)

Also: built-in.