Pharmaceutical compositions and methods for verifying dosing compliance

A pharmaceutical dosage form is provided that has a distinguishing characteristic and an identifier associated with the dosage form. The distinguishing characteristic is assigned from a limited set of distinguishing characteristics and is determined upon oral administration of the dosage form, or is detected in breath, bodily fluids, or tissues after ingestion, or injection or other non-oral administration. The identifier is associated with the dosage form and with the distinguishing characteristic. The identifier is associated with only one distinguishing characteristic but the distinguishing characteristic may be associated with multiple identifiers. The pharmaceutical dosage form may be used in a method to monitor compliance with a dosage regimen.