Coca Leaf

In Peru and Bolivia, coca leaves are chewed or brewed into teas; but they are also the raw material for cocaine.

According to US Customs and Border Protection, “It is illegal to bring coca leaves into the U.S. for any purpose, including to use for brewing tea or for chewing.” [link] 

Further Reading:

"How Coca-Cola Obtains Its Coca" New York Times [link]