Hi. thanks for asking in Healthcare Magic. Both Perocet and Roxicet contain a combination of Oxycodone and Acetaminophen (Paracetamol). Vicocet and Norco contain Hydrocodone and Acetaminophen. Morphine exerts its action by combining at three receptor (place where a drug attaches to the cell surface) sites namely mu, kappa and delta. But both Hydrocodone and Oxycodone are less effective than Morphine as they combine with only one receptor site (partial agonist). Morphine exerts its action directly ie., both the parent drug and its metabolite are effective. But the metabolites of Oxycodone (oxymorphone) and Hydrocodone (hydromorhone) are more effective than the parent drugs. The metabolites of Oxy and Hydrocodone are formed in the liver by an oxidative enzyme known as cytochromes. Alteration (polymorphism) in these enzymes will impair the metabolite production resulting in reduced action of these drugs. In Some persons, the rate of metabolism is enhanced (fast metabolizers) due to stimulation of cytochromes. Smoking can stimulate these enzymes. This will result in reduced actions and increased side effects. Diluadid contains Hydro morphone which is more potent (effective) than even Morphine. So, the reasons for your problem could be 1. Polymorphism of cytochromes (which could be identified by blood test through PCR techniques) resulting in lesser metabolites production and diminished action of drugs. 2. Stimulation of cytochrome enzymes resulting in increased metabolism that could be the reason for altered effect. Morphine and Hydromorphine are still effective for you as they don t need to be converted to its metabolites. I hope this is useful to you.