Final answer:
The source of drug-drug contraindication information in a computerized provider order entry system is the Drug knowledge database.
Step-by-step explanation:
The source of drug-drug contraindication information in a computerized provider order entry system is the Drug knowledge database. This database contains comprehensive information on drugs, including their interactions with other drugs. By accessing the Drug knowledge database, healthcare providers can determine whether two or more drugs should be avoided or used with caution due to potential harmful interactions.