And not just a little.
Scientists found that a diet drink mixed with your booze increased breathalyzer readings by a whopping 18%.
Sixteen people were followed as they hit the alcohol over a span of a few hours.
Each person was given a different mixture of regular soda, diet soda or a placebo as a mixer.
Then, each subject was tested after they had knocked back a few cocktails.
Within 40 minutes the group given low calorie drinks already had higher blood-alcohol levels.
More significantly, the diet soda group was above most states legal limit to drive after three to four drinks but the other groups were not.
Researchers think the difference comes from how the sodas were sweetened.
The sugar substitutes are believed to boost the effects of the liquor and intensify the effects.
That leaves drinkers with the age old quandary.
Use diet soda and stay marvelously thin but get wasted fast.
Or, bulk up with real cola but do a better job of holding your hooch.