Share on Pinterest
Experts say there is a difference between being awake and being alert. Andrii Afanasiev/EyeEm/Getty Images
  • Experts say caffeine can help you stay awake if you’re sleep deprived, but it probably won’t improve your performance on tasks.
  • They say caffeine is not a substitute for a good night’s sleep, which helps repair tissue and cleanse the brain.
  • They note that too much caffeine can also disrupt sleep patterns.

Caffeine may keep you alert enough to take on tasks if you’re short on sleep, but you probably won’t do them particularly well.

In a study published in the Journal of Experimental Psychology: Learning, Memory, & Cognition, a group of participants subjected to a night of sleep deprivation was asked to complete a reaction time test as well as a more complex “place-keeping” test, which required the completion of a series of tasks in a specific order without skipping or repeating any steps.

The researchers noted that caffeine did help in some instances.

“We found that sleep deprivation impaired performance on both types of tasks and that having caffeine helped people successfully achieve the easier task,” said Kimberly Fenn, PhD, an associate professor in the department of psychology at Michigan State University, in a press release. “However, it had little effect on performance on the place-keeping task for most participants.”

Fenn told Healthline that there is a simple takeaway from the study.

“Caffeine may be able to help you stay awake and pay attention to a task, but it does not help to prevent errors,” she said. “We are interested in procedural errors because they can be quite dangerous. For example, many medical professionals, such as surgeons, need to work long hours throughout the night.”

She also has some guideposts on what kind of tasks should be avoided if you’re short on sleep.

“I think the best way to conceptualize this is that one would not want to attempt any task that has consequences while sleep deprived,” said Fenn. “So I would caution against doing anything like driving or operating heavy machinery or performing any task in which an error could be significant. A good rule to follow is that you should not attempt any task while sleep deprived that you would not (or should not) attempt while intoxicated, irrespective of caffeine.”

Participants in the study either slept normally at home or were kept awake in a lab overnight.

They then consumed either a placebo or 200 milligrams (mg) of caffeine, approximately the amount in one to two cups of coffee (depending on the size of the cup and the strength of the coffee).

The findings support the theory that sleep deprivation impairs what’s known as “vigilant attention,” eroding the ability to complete cognitive tasks that require attention. It also underlines the need for essential workers to prioritize sleep, Fenn said.

“Caffeine can help you get through a midday slump, but it isn’t a substitute for a good night’s rest,” Dr. Anthony Puopolo, chief medical officer of the telemedicine company RexMD, told Healthline. “The importance of adequate sleep is especially relevant for individuals in high-functioning environments who often have to work long hours, such as doctors and truck drivers. A stable work-life balance can create better and safer outcomes for all. Understand your body’s needs and try to get as much rest as possible, when needed.”

Paul Serra, co-founder of Sleepline, says that while caffeine blocks adenosine, a neurotransmitter responsible for feeling tired, “good sleep offers so much more.”

“During deep sleep, the tissues in your body are repaired and your brain is cleared of plaque buildup,” Serra told Healthline. “During REM sleep, neural connections are formed and your memories are consolidated. Coffee or energy drinks can never replace what happens during good sleep.”

The caffeine found in coffee may keep drinkers awake but not necessarily alert, experts say.

“Caffeine covers up the symptom of feeling sleepy. It does not make the brain more rested, so it still does not allow the coffee drinker to function as well as they would if they were fully rested,” Ashley Olivine, a certified functional nutrition practitioner and sleep specialist, told Healthline.

About 62 percent of Americans drink coffee daily, according to Yurii Brown, a barista and founder of

Brown told Healthline that not only is coffee a poor substitute for sleep, overconsumption of caffeine — in excess of 400 mg daily — can disrupt sleep.

“It can impact the onset of sleep and reduce sleep time, efficiency, and satisfaction levels,” he said.

“In some cases, caffeine intake leads to tiredness and sleepiness. This is linked to the buildup of one of the brain chemicals, adenosine, which controls the sleep-wake cycle. Caffeine affects how the brain receptors react to the adenosine quantity, which results in a messed up sleep cycle — you might feel active at night, and tired during the day. Generally, it’s the continued intake of caffeine in high amounts that leads to poor sleep hygiene. The caffeine causes sleep deprivation, and that leads to sleepiness the following day.”

“If you’re a daily, regular caffeine drinker, your body may actually develop a tolerance to any sort of stimulatory effects,” added Conor O’Flynn of O’Flynn Medical, “so in effect, you will have to consume more if you want to experience any similar results. You’ve also got to consider the fact that coffee is a diuretic, which can leave you dehydrated and sleepy or sluggish.”

Fenn notes there are some benefits to drinking coffee and other liquids with caffeine.

“Caffeine is a central nervous system stimulant, so it increases alertness and energy,” she said. “This means that it can improve motivation and performance on some attention tasks and can reduce reaction time, or the time it takes to respond to a stimulus. There is also some evidence that caffeine can help to reduce anxiety. However, at high doses, caffeine can actually increase anxiety or cause jitteriness.”