Caffeine is a stimulant drug often used to improve mental processing. It is believed to work by blocking the neurotransmitter adenosine's receptors, increasing excitability in the brain. Caffeine also influences other neurotransmitters, including norepinephrine, dopamine, and acetylcholine. These have effects on mood and mental processing.
Effects of Caffeine on Mood
Caffeine increases alertness, and many people find that caffeine improves their mood through improving their sense of being switched on, and having a sense of task accomplishment. However, like other stimulants, it also increases anxiety. The effects of caffeine on mood are related to how the person expects the caffeine to make them feel, and to the context of the caffeine consumption, also known as set and setting.
So caffeine can provide a lift to your mood, but this is most noticable when your energy is already low. For many people, this is when you haven't had caffeine for a while, so some experts believe that the positive effects are actually simply a warding off of caffeine withdrawal. This is only partially true -- research shows that the positive effects of caffeine on mood occur in people who are not withdrawing as well as those who are. But for those who experience an increase in anxiety, the effects of caffeine on mood are unpleasant.
Effects on Mental Performance
Caffeine has been shown to improve performance on a range of different tasks, including vigilance, response times, information processing, and some -- but not all -- proofreading tasks.
But don't assume that it is worthwhile using caffeine as a shortcut to improving your performance. When comparisons are made between people whose daily intake of caffeine is low (up to 100 mg caffeine per day) and those who regularly consume a lot of caffeine (more than 300mg caffeine per day), we find that the improvements are quite small, and don't get better with more caffeine. While people who use a lot of caffeine every day do show improved performance with more caffeine, it may be that they are simply counteracting the effects of caffeine addiction -- so by taking more caffeine, they are getting closer to what their performance would be if they weren't addicted to caffeine in the first place.
Not sure whether your caffeine intake is high or low? Read about the amount of caffeine in foods and drinks.
And while there have been several studies showing that caffeine improves vigilance and reaction times, others exploring the subtleties of how this works have found that at least some of the time, this is an expectancy effect. Expectancy effects are a significant aspect of the effects that drugs have on people's perceptions and behaviors. People's expectancies of how caffeine will affect their performance -- in particular, if they think it will impair their performance -- seems to underlie some of the improvements in performance. In other words, if people think consuming caffeine will make their performance worse, they try harder and compensate for the expected effects of caffeine.
Is Caffeine a Good Way of Improving Mental Performance?
Overall, it probably isn't worth trying to enhance your performance by using more caffeine. The short-term benefit you may get from caffeine will be offset by increased anxiety while you are under the influence of caffeine, and when the effects wear off, withdrawal symptoms may worsen the very mental processes you are hoping to improve.
A better strategy for low users of caffeine, who drink the equivalent of one or two cups of coffee a day, would be choosing when to consume them, and timing your caffeine intake so that you are getting the stimulant effects, and not the withdrawal effects, before a task that requires your full attention. And remember, your performance could also be negatively impacted by caffeine.
If you use a lot of caffeine -- drinking the equivalent of more than three cups of tea or coffee per day -- it may be negatively affecting your health, so lowering your intake is worth considering.
Brunye, T., Mahoney, C., Rapp, D., Ditman, T., & Taylor, H. "Caffeine enhances real-world language processing: evidence from a proofreading task." Journal of Experimental Psychology: Applied 18:95–108. 2012.
Christopher, G., Sutherland, D. & Smith, A. "Effects of caffeine in non-withdrawn volunteers," Hum Psychopharmacol Clin Exp 20:47–53. 2005.
Harrell, P. & Juliano, L. "Caffeine expectancies influence the subjective and behavioral effects of caffeine," Psychopharmacology 207:335–342. 2009.
Koppelstaettera, F., Poeppelb, T., Siedentopfa, C., Ischebeckc, A., Kolbitschd, C., Mottaghye, F., Felberf, S., Jaschkea, W. and Krauseg, B. "Caffeine and cognition in functional Magnetic Resonance Imaging" Journal of Alzheimer’s Disease 20:S71–S84. 2010.
Rogers P., Heatherley, S., Hayward, R., Seers, H., Hill, J., & Kane, M. "Effects of caffeine and caffeine withdrawal on mood and cognitive performance degraded by sleep restriction." Psychopharmacology 179:742-752. 2005.
Smith, A Sturgess, W., & Gallagher, J. "Eff€ects of a low dose of caffeine given in different drinks on mood and performance," Hum. Psychopharmacol. Clin. Exp. 14:473-482. 1999.