Yes, with a caveat or two. He could fill it for cash provided it is not a refill of a controlled substance and is not too early to fill. Any other class of drugs that is a maintenance med or antibiotic would be fine if three reason for the insurance denial was too soon. If the prescription is for a drug that you've never taken before, then the pharmacist would probably fill it, unless it's for a schedule drug that is replacing another schedule drug that was recently filed. If the latter is the case, the pharmacist would probably call the doctor and get his reasoning for the new Rx. The doctor might be able to persuade your insurance company to set up an override for the denied claim in that situation.The reason I've said all this is that I've heard it all, and I've had many people all stiff like this while withholding critical information that would affect my decision on whether or not to fill the prescription.