Root beer is a sweet North American soft drink traditionally made using the sassafras tree Sassafras albidum (sassafras) or the vine Smilax ornata (sarsaparilla) as the primary flavor. Root beer may be alcoholic or non-alcoholic, come naturally free of caffeine or have caffeine added, and carbonated or non-carbonated. It usually has a thick, foamy head when poured. Modern, commercially produced root beer is generally sweet, foamy, carbonated, nonalcoholic, and flavoured using artificial sassafras flavouring. Sassafras root is still used to flavor traditional root beer, but since sassafras was banned by the U.S. Food and Drug Administration due to the controversially claimed carcinogenicity of its constituent safrole, most commercial recipes do not contain sassafras. Some commercial root beers do use a safrole-free sassafras extract.