Adulterant
Adulterants are chemical substances which should not be contained within other substances (eg. food, beverages, fuels or pesticides) for legal or other reasons. Adulterants may be intentionally added to substances to reduce manufacturing costs, or for some deceptive or malicious purpose. Adulterants may also be accidentally or unknowingly introduced into substances. The addition of adulterants is called adulteration.

# In food and beverages
Examples of adulteration include:
- Mogdad coffee, whose seeds have been used as an adulterant for coffee
- Roasted chicory roots were used for the same purpose, starting during the Napoleonic era in France (and still is a moderately popular additive there for cheaper coffee)
- Roasted ground peas, beans, or wheat used to adulterate roasted chicory
- Diethylene glycol, used by some winemakers to fake sweet wines
- Oleomargarine or lard, added to butter
- Rapeseed oil, commonly added to sunflower oil and soybean oil, brassicasterol being a marker of its presence
- Rye flour, corn meal or potato starch used to dilute more expensive flours; alum is also added to disguise usage of lower-quality flour
- Apple jellies were substituted for more expensive fruit jellies, with added colorant and sometimes even little pieces of wood that simulated strawberry seeds
- Artificial colorants, often toxic - eg. copper, zinc, or indigo-based green dyes added to absinthe
- Sudan I yellow color, added to chili powder
- Water, for diluting milk and beer and hard drinks
- Lower-quality black tea disguised as higher class
- Starch, added to sausages
- Cutting agents are often used to adulterate (or "cut") illicit drugs, for example shoe polish in solid cannabis
- Urea and other non-protein nitrogen sources added to protein products in order to inflate crude protein content measurements
- Powdered beechnut husk aromatized with cinnamic aldehyde may be marketed as powdered cinnamon.
- High fructose corn syrup can be used to adulterate honey.

# History
Historically, usage of adulterants has been common in free market societies with few legal controls on food quality and/or poor or nonexistent monitoring by authorities; sometimes this usage has even extended to exceedingly dangerous chemicals and poisons. In the United Kingdom during the Victorian era, adulterants were quite common; for example, cheeses were sometimes colored with lead. Similar adulteration issues were seen in industry in the United States until the passage of the Pure Food and Drug Act in 1906. More recently, adulterant use in the People's Republic of China has inspired much public attention. (See: Food safety in the People's Republic of China).
Adulterant usage was first investigated in 1820 by the German chemist Frederick Accum, who identified many toxic metal colourings in food and drink. His work antagonised food suppliers and he was discredited by a scandal over his alleged mutilation of Royal Institution library books. The physician Arthur Hill Hassall later conducted extensive studies in the early 1850s, which were published in The Lancet and led to the 1860 Food Adulteration Act and subsequent further legislation.
At the turn of the twentieth century, industrialization saw an uprise in adulteration and this inspired some protest.  Accounts of adulteration led the New York Evening Post to parody:
Mary had a little lamb,
And when she saw it sicken,
She shipped it off to Packingtown,
And now its labeled chicken.

# In drug tests
Adulterants can be also added to urine, in order to interfere with the accuracy of drug tests. They are often oxidative in nature - hydrogen peroxide, and bleach have been used, sometimes with pH-adjusting substances like vinegar or sodium bicarbonate.  These can be detected by drug testing labs, but some of the less expensive tests do not look for them.

# Notable incidents of adulteration
- In 1987, Beech-Nut paid $2.2 million in fines for violating the Federal Food, Drug, and Cosmetic Act by selling artificially flavored sugar water as apple juice. 
- In 1997, ConAgra Foods pled guilty to federal criminal charges that one of its units illegally sprayed water on stored grain to increase its weight and value. 
- In 2007, samples of wheat gluten mixed with melamine, presumably to produce artificially inflated results from common tests for protein content, were discovered in many U.S. pet food brands, as well as in the human food supply. This adulterated gluten was found to have come from China, and U.S. authorities concluded that its origin was the Xuzhou Anying Biologic Technology Development Company, a Xuzhou, China-based company. (See: Chinese protein export contamination.)