In what situation can a pharmacist refuse a partial fill of a prescription for controlled substances?

A pharmacist can refuse a partial fill of a prescription for controlled substances if the prescription does not have an indicated refill. This is because regulations governing controlled substances require that any partial fill must still comply with the original prescription’s directives, including the number of refills allowed by the prescribing physician. If a prescription does not indicate any refills, the pharmacist is not authorized to dispense any part of the original prescription after the first fill, which means no partial fill can occur.

In contrast, factors such as a patient's allergies to ingredients do not influence the pharmacist's ability to fill a prescription partially, as these concerns are addressed through appropriate therapeutic substitutions or patient counseling. Additionally, a prescription written over a year ago may not be valid for filling, but it does not specifically relate to the pharmacist's ability to disallow a partial fill. Lastly, even if a patient requests a quantity larger than prescribed, the pharmacist retains the authority to adjust the fill according to the prescription while still being within the bounds of dispensing rules, but this does not directly relate to the issue of partial fills.