Warning! Although a copper mug is traditionally used to serve a Moscow Mule, it can be toxic. The drink is acidic (vodka, lime juice and ginger beer) and can leach copper from an unlined copper mug. Continuous use can lead to nausea, diarrhea, headaches, dizziness and irritation of the mouth, nose and eyes. Mugs lined with nickel or stainless steel are safe. (Bottom Line Personal)