Lil Wayne,I Drank Sizzurp'Because I Was Sick'

Lil Wayne is finally admitting he had a substance abuse problem -- claiming he would frequently pound a codeine-based drink called sizzurp because he was "sick."

Wayne just spilled his guts in a new documentary-style video shot by one of his friends -- saying he first started drinking the stuff when he was a kid because one of his idols, Pimp C, would often rap about it.

But Weezy claims he relied on sizzurp as he became more famous -- saying he needed the drink to help him cope with the pressure of being a celebrity.

Wayne insisted he quit using the stuff last year -- and in the video he explains he no longer needs it because, "I'm not sick anymore."

As for Pimp C -- he died from an accidental sizzurp overdose in 2007.