INERT INGREDIENTS FUNCTIONS AND COMMON IMPURITIES
"Some Inert Ingredients ,(AKA excipients)comprise the product's delivery system. These transport the active drug to the site in the body where the drug is intended to exert its action. Others will keep the drug from being released too early in the assimilation process in places where it could damage tender tissue and create gastric irritation or stomach upset. Others help the drug to disintegrate into particles small enough to reach the blood stream more quickly and still others protect the product's stability so it will be at maximum effectiveness at time of use. In addition, some excipients are used to aid the identification of a drug product. Last, but not least, some excipients are used simply to make the product taste and look better. This improves patient compliance, especially in children. Although technically "inactive" from a therapeutic sense, pharmaceutical excipients are critical and essential components of a modern drug product. In many products, excipients make up the bulk ...They are classified by the functions they perform in a pharmaceutical dosage form. "
from ipecfoundation.org
Excipients rarely posses pharmacological activity and are categorized as "inert."
However, excipients may have functional groups that can initiate, participate in chemical or physical interactions possibly leading to compromised quality of your product thereby degradation of the active ingredient


COMMON IMPURITIES OF VARIOUS INERT INGREDIENTS (EXCIPIENTS)
Also, excipients can be a source of microbial contamination. See below for common impurities found in some excipients
Starch---Formaldehyde
Lactose---Aldehydes, reducing sugars
Benzyle alcohol---Benzoldehyde
Stearare lubricants---alkaline residues etc
povidone and crospovidone-peroxide