Which of these is used as the key ingredient in home-brewed root beer in the United States?

Sassafras roots are used to make traditional root beer, although they were banned for commercially mass-produced foods and drugs by the FDA in 1960.

Laboratory animals that were given oral doses of sassafras tea or sassafras oil that contained large doses of safrole developed permanent liver damage or various types of cancer.

In humans, liver damage can take years to develop and it may not have obvious signs. Along with commercially available Sarsaparilla, sassafras remains an ingredient in use among hobby or microbrew enthusiasts. While sassafras is no longer used in commercially produced root beer and is sometimes substituted with artificial flavors, natural extracts with the safrole distilled and removed are available.