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from the Starbucks site:

+Made with natural ingredients like real fruit and fruit juice plus caffeine from green, unroasted coffee beans, both handcrafted Refreshers™ are a delicious way to kick back and cool off.

*Starbucks Refreshers Very Berry Hibiscus:

+ Tangy, whole blackberries combined with the taste of hibiscus and sweet berries make for one unbelievably chill summer treat.

Comment - I don't think you'll be able to replicate the caffeine from green coffee beans, but you could brew a nice hibiscus tea (use Red Zinger or dried hibiscus flowers carried at many natural foods or latino markets) and then mash up some blackberries. You may want to experiment with green tea if you want the caffeine boost.

Starbucks Refreshers Very Berry Hibiscus