Yes, DEPENDENT is a Scrabble word!

Letter values in Scrabble US: D 2, E 1, P 3, E 1, N 1, D 2, E 1, N 1, T 1.

Is it a valid word?

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

a person who relies on another person for support (especially financial support)

relying on or requiring a person or thing for support, supply, or what is needed
contingent on something else
(of a clause) unable to stand alone syntactically as a complete sentence
held from above
being under the power or sovereignty of another or others
addicted to a drug

Also: drug-addicted, strung-out.