A new study in the Journal of Experimental Psychology tested how caffeine and sleep can impact your day and overall effectiveness at completing tasks. Experts revealed that caffeine can help you stay awake if you’re sleep-deprived, but it likely won’t improve your performance on tasks.

Caffeine can help you get through the midday slump, but it isn’t a substitute for a good night’s sleep. Sleeping is needed to help repair body tissue and cleanse the brain of plaque buildup. Adequate sleep is especially important for people in high-functioning work environments who work long hours, such as medical professionals and truck drivers. Also, not only is coffee a poor substitute for sleep, but overconsumption of caffeine—more than 400 mg daily—can also disrupt sleep.

Awake doesn’t necessarily mean alert. Sleep deprivation impairs your ability to complete cognitive tasks that require attention. A simple rule is that you shouldn’t attempt any task while sleep-deprived that you would not (or should not) attempt while intoxicated.