There has been a lot of talk, and clickbait articles about a California man charged with DUI, when the only 'drug' in his system was caffeine.
The real situation (Snopes.com) is that he was allegedly driving erratically, and acting as if he were somehow impaired, and the police started an investigation based upon that.
The police ordered lab tests, which came back only showing caffeine; and the charges ended up being changed to Reckless Driving.
So, that one case aside, can someone be charged with a DUI for too much coffee?
Driving under the influence.
(1) A person is guilty of driving while under the influence of intoxicating liquor, marijuana, or any drug if the person drives a vehicle within this state: (c) While the person is under the influence of or affected by intoxicating liquor, marijuana, or any drug;
"The FDA says that caffeine is both a drug and a food additive."
So, yes it's possible to be charged with DUI for only excessive caffeine, but realistically, it's not going to happen. If it does happen in Washington, call me, and I'll give you a good price on representation.
also take note from that FDA article:
"Caffeine doesn't make a drunk person sober or fit to drive – it DOES NOT get rid of the effects of alcohol."
It also won't lower your BAC (Blood Alcohol Content), and there is some evidence that mixing caffeine and alcohol actually makes it worse.