Pharmacists also check (whenever possible) for excess usage, misuse, etc., and can decline to fill prescriptions in those instances. They usually discuss the situation with the doctors, but they do, in fact, have the authority to refuse to fill them.

My partner is a pharmacist. Situations like that happen quite frequently. Patient tries to fill multiple prescriptions, patient brings in scripts from multiple doctors, patient tries to refill before eligible dates, etc. Checking for those things is a significant role in their jobs.