Copper mugs used in trendy cocktails like Moscow Mules may be giving people more than a hangover. Health officials in Iowa say the popular copper cups can give their users food poisoning.

The state's Alcoholic Beverages Division made the declaration after examining the poisonous nature of copper and copper alloys mixing with food. According to the Food and Drug Administration's Moral Food Code, copper is prohibited from coming into direct contact with foods that have a pH below 6.0.

Liquids with a pH below 6.0 include vinegar, fruit juice and wine. Cocktails like the Moscow Mule, which are widely served in copper mugs and include lime juice, fall far below this standard. The warning comes as the Mule has risen in popularity with social media users, who enjoy posting pictures of the attractive mugs.

#MoscowMule..love you to the beach and back.💙🏝🌊 #fridayfriendswithcooper A post shared by Moscow Mule (@the.moscow.mule) on Aug 4, 2017 at 6:40pm PDT

"When copper and copper alloy surfaces contact acidic foods, copper may be leached into the food," according to the Alcoholic Beverages Division's statement. Copper poisoning can lead to stomach pains, diarrhea, vomiting and even yellowing of the skin.

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The health warning does note that copper mugs that have an inner lining using a different metal like nickel or stainless steel are safe to drink from.