My mom combined oxycodone with morphine, what are the possible drug interactions?

Additive: There really arent drug "interactions" per se. One plus one equals two with these drugs, depending on the dose taken. These drugs generally should NOT be used together - if your mother is being prescribed these medications, a consultation from a trained pain physician might be helpful. If they are NOT prescribed, she shouldn't be taking them, and the addition of one to the other may be dangerous.