The Alcoholic Beverages Division of the State of Iowa is concerned with the interaction of those contents with the copper mug and issued an advisory bulletin in late July to warn of potential health risks. When the copper or copper alloys come into contact with food or liquid with a pH below 6, the copper can leach into it.
"The goal of this bulletin is to advise licensees and permittees selling and serving alcoholic beverages in copper mugs of the applicable federal guidance and state regulations regarding the use of copper and copper alloys in contact with food and beverages", the statement reads. So you might be taking in a concentration of copper along with your cocktail. Made of vodka, lime, and ginger beer, the acidic combination of a Moscow Mule means it should not be served in a pure copper mug, according to Live Science. Examples of these acidic foods include fruit juice, wine, vinegar - and Moscow Mules.
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.
High levels of copper are poisonous and can cause food poisoning.
Copper poisoning, similarly to lead or other metal poisoning, occurs after a period of exposure.
According to the National Institutes of Health, symptoms of copper poisoning include abdominal pain, diarrhea, vomiting, and jaundice.