Oh no. I could not resist.
Today most doctors receive sample quantities of prescription drugs from makers that they then dispense to their patients.
That is all quite legal. It is also legal for the doctor to write a prescription in his own name. Take it to a pharmacy, have it filled and then dispense it to patients.
I strongly suspect this is what was done.. it was done to keep some pharmacist from telling the world Rush filled a prescription for Viagra.
There would be nothing illegal in doing it. Someone was out to get Rush on drugs and did not get it done.