Well, according to
this source, Citalopram inhibits Cytochrome P450. Oxycodone is a
substrate of CYP450, however, it is metabolized by enzyme CYP3A4, wheras citalopram inhibits CYP450 and CYP2D6. Oxycodone
IS effected weakly by CYP2D6, though according to
this article, the increase in blood levels is pretty insignificant. However, when Oxycodone is taken in combination with a Cytechrome P450 CYP3A4 inhibitor, the levels of oxycodone increase significantly.
So you're probably safe taking the two medications, though I would definately look into it more thoroughly. From what I found, Citalopram works on CYP2D6,
NOT CYP3A4. Fluoxetine and fluvoxamine will work on CYP3A4, as well as a number of other antidepressants/medications that you can again see
here.