Coumarin is a chemical compound which is found naturally in some plants, although it can be synthetically produced as well. It has a distinctive odor which has led people to use it as a food additive and ingredient in perfume. Due to concerns about coumarin as a potential liver and kidney toxin, its use as a food additive is heavily restricted, although it is perfectly safe to eat foods which naturally contain coumarin.

The chemical name for coumarin is benzopyrone. The distinctive sweet odor reminds many people of freshly cut grass or hay, and it has been used in perfumes since the late 1800s. In a pure form, coumarin has a crystalline structure, and it is said to taste faintly like vanilla. When ingested, coumarin acts as a blood thinner, and it also appears to be effective in treating some tumors. Coumarin has fungicidal properties as well. However, other much safer substances can be used for all of these purposes, although coumarin is sometimes used in combination with other blood thinners for medical treatment.

One natural source of coumarin is tonka beans, tropical beans which are known by the French as coumarou. To release their captive coumarin, the beans are soaked in alcohol and then fermented. Coumarin also occurs in sweet clover, strawberries, cherries, bison grass, woodruff, and apricots. Coumarin has traditionally been used as a vanilla substitute in various foods, especially tobacco, although this usage is restricted in some countries.

Some traditional foods are made with plants which contain coumarin, and coumarin is clearly an important flavor compound in the food since these foods are prepared in a way which concentrates the natural coumarin. In both Poland and Germany, plants like woodruff are added to alcohol to make a beverage with a distinctive fresh, spring-like flavor which can probably be credited to the coumarin. These products are not generally dangerous to consume, although people may want to avoid consuming high volumes of these foods; the same goes for therapeutic coumarin or coumarin derivatives which may be prescribed by a doctor.

In plants, coumarin appears to act as a natural pesticide, cutting down on insects so that the plant can grow undisturbed. Some chemicals in the coumarin family have been harnessed for their pesticide uses, and some related chemicals are even used for larger pests like rodents. Consumers may be familiar with one chemical in the coumarin family; warfarin is a popular anticoagulant which can be ingested or injected, depending on the needs of the patient.