Inactive ingredients refer to any components in a drug other than the active ingredient. They could be auxiliary substances added to pharmaceutical formulations to enhance the therapeutic effect of the drug by improving its characteristics, such as stability, solubility, and bioavailability, in order to better meet the needs of patients.

Inactive ingredients, or in this context, pharmaceutical excipients, have been used in approved drugs for specific routes of administration, therefore are typically no longer considered new ingredients. In practice, it can be assumed that the use of such ingredients is safe for use in a similar manner and type of product. When these inactive ingredients need to be incorporated into new drugs, less scrutiny may be required during the approval process.

The TargetMol Inactive Ingredient Library comprises 182 inactive ingredients from FDA-approved drugs, and is a valuable tool for drug development.