– One of the most talked-about cocktails this week is the trendy Moscow Mule, but for all the wrong reasons. You can thank Iowa. The spate of headlines was kicked off by an official state health advisory warning that the drink, usually served in a copper mug, poses a health risk if the wrong kind of mug is used. For the uninitiated, a Moscow Mule has vodka, ginger beer, and lime, and thus is acidic, explains Live Science. The problem is, you're not supposed to serve acidic beverages in mugs with a copper interior because it raises the risk of copper leaching into the drink. Solution? A mug with a copper exterior is fine, but make sure the interior is made of stainless steel, nickel, or some other alternative. The advice isn't new, but the state felt compelled to issue the advisory given the "recent popularity of Moscow Mules." (A cruise through Instagram proves the point.) Iowa's warning is based on an FDA advisory from a few years ago. Specifically, it says that drinks with a PH level of 6.0 or under should not be served in pure copper mugs, and the Mule falls into that category. For the record, so do fruit juices, vinegar, and wine, notes the Daily News. (Some might prefer a little food poisoning to this cocktail ingredient.)