In 2015, Joseph Schwab swerved in front of an ATF officer on a California highway. As the officer watched, Schwab continued “erratically weaving in and out of traffic almost causing several collisions.” The officer was convinced Schwab was driving under the influence. Even after a breathalyzer found his blood alcohol content zero, the officer arrested him and ordered a toxicology report. The result? Schwab was clean of everything except for caffeine.

Alcohol-related DUIs are usually relatively simple: If your BAC is above 0.08%, you’re legally inebriated, and thus driving under the influence. But what about substances? If an officer can testify that a substance impaired your ability to safely operate your vehicle, they can charge you with a DUI. And it doesn’t matter what that substance is.

On the surface, this appears to make sense. If a driver smoked a ton of weed and can’t safely navigate the road, they are breaking the law. The same is true even for prescription drugs such as painkillers or muscle relaxants.

So could caffeine ever land you a DUI?

The Legal Match Blog says yes: It is possible that an officer could testify you were unsafe to drive and slap you with a ticket–even if all you’d been doing was pounding coffees. There’s no illegal BAC for caffeine. But if you’re impaired–and not driving as well as a sober person would–you’re breaking the law.

So could a caffeine-related DUI actually stick?

This is a more complex question. Schwab, for example, was charged with a DUI. The prosecutor didn’t claim this substance was caffeine, specifying it might have been something the toxicology report couldn’t detect. But various news outlets ran with a caffeine-DUI story.

As Legal Match argues, “Prosecutor would be hard-pressed to prove to a jury beyond a reasonable doubt that the consumption of caffeine, alone, inhibited Schwab’s abilities to drive enough to pose any danger.” And sure enough, the California prosecutor dropped Schwab’s case.