Tonka beans have been used as a source of natural coumarin, and, after its synthesis in the 1940s, artificial coumarin became one of the first artificial flavoring agents as a vanilla substitute. However, the importation of natural tonka beans in the US has been banned by the FDA since 1954 because the bean has shown toxicity in extremely high concentrations. Since the ban, the product has been frequently imported illegally into the United States by gastronomic enthusiasts. There have been calls for removing the restrictions on the use of tonka beans in food in the U.S. similar to the successful deregulations of mangosteens and absinthe in the early 21st century; the regulations are criticized as unreasonable due to the unlikelihood of consuming enough coumarin to cause ill effects and due to the presence of coumarin in unregulated foods.