...one use(smoking) is probably fine, but extending use through smoking/IV/and to a lesser extent, snorting may lead to tiny particles from the pills binders getting stuck in your lungs. Of course this leads to all sorts of nasty...
People say swallowing OC works, but I've always been able to get MUCH higher through snorting.
Comparing oxy and heroin? Since I don't IV, I can't give you a comparison from that perspective, snorted, however...
Oxy is more of rush, one's being is filled with energy and social thoughts. Slight euphoria, I don't nod unless I take 100mg or more.
H is kind of an "ahhhhhh" close your eyes and count to 1,000 type of high(snorted). Weak, but noticeable rush...very sedating, not as much euphoria, imo...if you like the nod...choose H.