You are correct in your statement that killing someone is not the moral equivalent of a prescription drug addiction. However, once Rush began to take pills that were not actually prescribed by his doctor but were obtained from people who were not licenced pharmacists the drugs he was taking ceased to be prescription drugs.
Hopefully, Rush has beaten or will beat his addiction but during his treatment there is no difference between someone that is addicted to drugs that are sometimes prescribed by a doctor and someone that is addicted to illicit drugs.
Is there some significant point in that sentence that you were trying to make. If so, it didn't reveal itself.