It's a common technique: ordering a cup of joe after a night of drinking to try to perk up.

But a new study shows caffeine can fool you into thinking you're sober when you're not -- and that can make you more vulnerable to making poor decisions.

"Well that's kind of scary because a lot of people do probably drink coffee after drinking, thinking it's going to wake them up to drive home," said Jennifer Wilson, who describes herself as a social drinker.

The study, published in the Behavioral Neuroscience journal, involved mice injected with both alcohol and caffeine. The mice were definitely alert, but still couldn't avoid traps where they got shocked.

Some said coffee after drinking could have another side effect.

"As far as I'm concerned, more caffeine just keeps you up later so you keep drinking later," Dallas resident Taylor Howard said.

Mothers Against Drunk Driving said it hopes the news prevents even perky drinkers from driving.

"It's one of those old wives' tales that circulates around -- that coffee will sober you up like a cold shower," said Mary Kardell, executive director of MADD North Texas. "But the truth is the only thing that will help is time."

Wilson said she'll think twice before drinking and getting caffeinated.

"Everyone on the roads together, after drinking, and then having coffee ... it could be very dangerous," she said. "Hopefully this study gets the word out, and people are more aware of this."