The story of the Moscow Mule is muddled, but rumor has it that one night in a bar back in the 1940s, the heads of Smirnoff wondered what would happen if they combined their vodka with their buddy’s ginger beer and the squeeze of a lemon, and boom: Moscow Mule. As for the origin of the iconic copper mug that traditionally houses the cocktail, one historian says the ginger beer maker’s girlfriend had recently inherited a business that produced copper goods, and naturally wanted in on the action.

The jury’s out whether or not the copper actually has any real merit; some believe the metal supposedly adds an extra chill to the already cold booze. Regardless, we’ve been drinking the classic cocktail every summer since then, and now a bunch of scientists are here to ruin all the fun.

The Alcoholic Beverages Division of the State of Iowa—the lamest Alcoholic Beverages Division out of all the states—recently released an advisory reminding everyone that copper is a reactive metal, which means it can creep into the contents of whatever it comes in contact with, provided that food or beverage has a pH level below 6.0, such as vinegar, fruit juice, or wine.

And hey, guess what has a pH level of “well below” 6.0, according to the advisory? That would be the Moscow Mule, thanks to its super-acidic ginger beer and lemon juice. Thus, you shouldn’t use a copper-lined mug in accordance with it, say the buzzkills from the Hawkeye State.

High concentrations of copper are poisonous and have caused foodborne illness, they say. But if you’re wondering why you’ve never experienced diarrhea, abdominal pain, vomiting, and the works after drinking many Moscow Mules in your life, that’s because you probably didn’t ingest enough copper for it to leave any kind of damage.

According to the U.S. Food and Drug Administration (FDA), you’d need to consume large amounts of copper before poisoning comes into play. Plus, many copper mugs are actually lined with non-reactive metals like stainless steel, so there’s a good chance your friendly neighborhood bartender is looking out for you and your health and has long since made the switch.

If you want to be super diligent and completely eliminate your risk of getting the copper-induced shits, you can drink your Moscow Mule out of a regular old glass. Just know that you won’t look nearly as cool.