oxycodone is metabolized by the cytochrome isoenzyme CYP2D6 of the liver

CYP1A2, CYP2C9, CYP2C19, CYP2D6, and CYP3A4

It removes all your toxic waist

Yes. However, citalopram will pretty much negate the effects of the codeine, and vice versa.
Citalopram is CYP2D6 inhibitor, while codeine is a substrate.
So you wont feel the codeine, or the citalopram.
So I'd not do the codeine. You could try it though, if its not dangerous for you to not be on the citalopram.

Ref http://en.wikipedia.org/wiki/Cyp2d6#CYP2D6_Ligands

Cytochrome P450 and CYP2D6 allow codeine to undergo O-demethylation to form morphine.