Historically, Tannic acid was used along with activated charcoal and magnesium oxide in the “universal antidote,” formerly used for poisoning. These three ingredients in combination were believed to work better at absorbing poisons than any of the ingredients alone. Unfortunately, the activated charcoal soaked up the Tannic acid, more or less inactivating it. This made the combination less effective.
Tannic acid is also taken by mouth and applied directly for bleeding, chronic diarrhea, dysentery, bloody urine, painful joints, persistent coughs, and cancer.
In foods and beverages, tannic acid is used as a flavoring agent and is far more widespread and significant amounts are used as process aids in beer clarification, aroma compound in soft drinks and juices. Equally important are applications in the wine industry, where it finds use as a natural clarifying agent, color stabilizer and taste enhancer. In many parts of the world such uses are permitted. In the United States, Tannic acid is classified as and generally recognized as safe by the Food and Drug Administration.
In manufacturing, tannic acid is used in ointments and suppositories for the treatment of hemorrhoids; for tanning hides and manufacturing ink; and to kill dust mites on furniture.
Tannins are a basic ingredient in the chemical staining of wood, and are already present in woods like oak, walnut, and mahogany. Tannic acid can be applied to woods low in tannin so chemical stains that require tannin content will react. The presence of tannins in the bark of redwood (Sequoia) is a strong natural defense against wildfire, decomposition and infestation by certain insects such as termites.