substance found within other substances, although not allowed for legal or other reasons

An adulterant is a chemical substance that should not be present in other substances, like food, drinks or fuels. Adulterants are often added to more expensive substances to increase the visible quantity. The word is used when the addition is unwanted by the recipient of the product. Chemical substances that are added to food or drinks for a purpose are called food additives. When substances are added to (illegal) drugs, these are often called cutting agents.