First of all, get over it. Mate de Coca is tea made from the Coca leaf and although difficult to obtain is legal -- even in the USA.
Most eating establishments in the Andes will have a bowl of coca leaves placed next to other teas and coffee.
The effect of Mate de Coca is something like that of Guaraná, a soft stimulant without the harshness of caffeine.
The illustration above was done in 1897 by Franz Eugen Köhler. The photograph above is of a coca plantation in Peru.
There are several traditional uses for Coca; chewing (with ashes of the quinoa plant), tea, and the making of narcotics for North Americans. Here we address only the tea use. It has been reported that Coca-Cola imported 204 tons of coca leaf into the USA in 1996 - using it as a flavoring in its soft drink. Annual import figures are difficult to obtain.
Mate de Coca is made just like any other tea. It can be made with a brew of whole leaves steeped in hot water or you can buy it in a crush form, often in tea bags.