According to a spokesperson from the Centers for Disease Control (CDC), LaKia Bryant, be careful what material if any was used to line your Moscow Mule mug. Because of the ingredients, Moscow Mules are acidic. Acidic drinks can leach copper from unlined copper mugs. If you are experiencing nausea, diarrhea, headaches, dizziness or mouth, nose and eye irritation, you may not be having a hangover. Long term exposure to the copper can cause these same issues.
Make sure your mugs are lined with other metals such as nickel or stainless steel to eliminate the copper from leaching into your drinks.