back in the day when I first started using oxycontin I was doing doses of 20mg and 30mg to nod. when I started taking zoloft I noticed that I had to double my oxy dose to get high. could've just been my tolerance and it was coincidence that it happened at the same time, or it could've been that the zoloft just made have to take more oxy.
but, I will note that I didn't need to be on SSRIs, theres something about them that make me manic. like crazy psycho manic, so maybe if you need them, they won't bother your dose. but I was put on them when I went to the doctor to try to get xanax.