How do we know there was no equagesic present in May?

In May, did Bruce's doctors come to any solid or official conclusion as to what caused Bruce's problems? If they had why would Bruce've gone all the way back to LA for testing (I understand he may not've liked his doctor suggesting that his cannibis use could be the problem, but did they tell him with no uncertainty that it was?)? Did they even consider equagesic as a possibility at that time? If the medicine was already in his bloodstream by the time he was being treated how would they have known about it? Isn't it possible that he had used it & they didn't know? Perhaps he himself didn't think it was relevant, assumed that it being a prescription drug (in a small dose) would be harmless? I don't know myself, but I'm asking how you know it was or wasn't so.