Iowa officials issued an advisory over the rise in popularity of the drink, Moscow Mule — a drink that is traditionally served in a copper mug.
CBS News reports the state has adopted the Food and Drug Administration’s Model Food Code. The code says copper is prohibited from coming into direct contact with foods with a pH below 6.0.
According to the advisory, the pH of the drink is well below 6.0.
A Moscow Mule contains vodka, ginger beer, lime juice and a lime wedge, according to Allrecipes.
The advisory says when copper surfaces contact acidic foods, copper may be leached into the food. High concentrations of copper are poisonous and have caused foodborne illness.
Iowa’s Alcoholic Beverages Division says copper mugs with a stainless steel or nickel lining are safe to use.