That is not an easy question to answer. My understanding is that they are very close to each other in potency but their effectiveness can differ depending on how you react to each of them.
Both act on opioid receptors in the brain. There are several different kinds of opioid receptors; some research suggests that oxycodone effects more types of opioid receptors than morphine does - suggesting that it could be stronger.
But different people have different levels of these receptors. If you have more of the opioid receptors that morphine acts on then morphine might be stronger. If you have more of the receptors that oxycodone acts on then it might work better.
To complicate matters the levels of these receptors can differ depending on where in the body the injury has occurred. If you have an abdominal injury a recent study suggested that oxycodone would probably work better because more oxycodone reactive receptors are found in the gut.
This is an evolving area of pain medicine - researchers are slowly figuring out how just who reacts best to which pain medication.
The best thing to do is to try a drug and see how it works; if it doesn't work to your satisfaction or if you have to use really high levels of it to relieve your pain ask your doctor to try another one. You might be able to find a drug that is better fitted to your body.
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