Caffeine and IQ: Does Coffee Make You Smarter?

Caffeine does not raise IQ. A dose of caffeine reliably speeds reaction time and lifts alertness for a few hours, and a genetic study of up to 415,530 adults, sensitive enough to detect a long-term effect smaller than 1 IQ point per daily cup of coffee, found no sign that a coffee habit changes cognitive ability in either direction.

The caffeine IQ question has two halves. One is acute: does a cup of coffee before a test make you sharper that day? The other is habitual: do regular coffee drinkers end up with better or worse minds over the years? This page covers what controlled trials show for each, why much of the short-term "boost" turns out to be relief from withdrawal, what to make of caffeine before an IQ test, and where the evidence is thin. IQ-point conversions use the standard 15-point standard deviation and are approximate.

Caffeine works by blocking receptors for "adenosine", a chemical that builds up in the brain during waking hours and promotes sleepiness. The most thorough recent summary is a 2016 review by McLellan, Caldwell and Lieberman in Neuroscience and Biobehavioral Reviews, written by researchers with long experience studying caffeine use in the military. They concluded that low to moderate doses, roughly 40 to 300 mg, improve alertness, vigilance, attention and reaction time. Effects on memory and on higher-order executive functions such as judgment and decision making were much less consistent.

An earlier review by Astrid Nehlig (2010) reached a similar conclusion. Caffeine usually did not improve learning or memory, it helped working memory only to a limited extent and could hinder tasks that lean heavily on it, and most studies found faster reaction times. Nehlig's summary was that caffeine is a mild stimulant whose cognitive effects come largely from its indirect action on arousal and mood, and that it cannot be considered a pure cognitive enhancer.

The clearest benefits appear when people are tired. In a 2015 trial, 20 Special Forces soldiers working through three successive nights, with only 4-hour sleep periods in the afternoons, were randomly assigned to caffeine or placebo. The caffeine group stayed faster on vigilance tasks and answered a logical reasoning test more quickly. That is a real and useful effect, and it is an effect of restoring performance that sleep loss had taken away. The soldiers were not reasoning at a higher level than they could when rested.

Most adults who volunteer for caffeine studies already consume it daily. If they are asked to skip their morning coffee before testing, they arrive mildly withdrawn, sleepier and slower than usual. Giving them caffeine then improves their scores against a placebo group, but part or all of that improvement may simply be the reversal of withdrawal.

Peter Rogers and colleagues tested this directly in a 2013 study titled "Faster but not smarter." They compared 212 medium-to-high caffeine consumers with 157 people who consumed little or none, giving each group caffeine or placebo under double-blind conditions after overnight abstinence.

• Habitual consumers: Overnight withdrawal made them sleepier and less alert, and slower on simple and choice reaction time and worse on a recognition memory task by the afternoon. Caffeine brought these measures back up.

• Non-consumers and low consumers: Caffeine reduced sleepiness, but it had little effect on mental alertness or mental performance, because it also caused a substantial rise in anxiety and jitteriness that offset the benefit.

• Both groups: Caffeine sped up finger tapping and reaction times, a motor effect that did not depend on habitual use.

The authors concluded that because tolerance develops to caffeine's effect on sleepiness, frequent consumption fails to enhance mental alertness and performance. A 2005 review by James and Rogers had already argued that, in appropriately controlled studies, the apparent benefits of caffeine on performance and mood are almost wholly attributable to reversing the adverse effects of short periods of abstinence. Not every researcher accepts the strongest version of that claim, and the McLellan review notes benefits in sleep-restricted conditions. Both camps agree on the part that matters for IQ: caffeine makes people faster and more alert, with no good evidence that it improves the reasoning that intelligence tests measure.

Observational studies of coffee and cognition have produced scattered results. In the Rancho Bernardo study of 1,528 older Californians, women with higher lifetime coffee intake scored better on 6 of 12 cognitive tests after adjustment, while men showed no relationship at all and decaffeinated coffee showed none in either sex. Findings that appear in one subgroup and on some tests are hard to interpret, because coffee drinking tracks income, health, smoking and social habits that also relate to test scores.

"Mendelian randomization" offers a way around that confounding. The method uses genetic variants that nudge how much coffee people drink. Because those variants are assigned at conception, they are not tied to education or lifestyle, so they act as a natural experiment. Zhou and colleagues (2018) applied this design to up to 415,530 participants of European ancestry in 10 cohorts, including the UK Biobank. Gene variants linked to drinking more coffee showed no association with global cognition or memory, and in the UK Biobank they showed none with reaction time or a reasoning test either. The study had the statistical power to detect an effect of about 0.045 standard deviations per daily cup, roughly 0.7 IQ points, and found nothing. The authors noted that this also argues against coffee harming memory in mid to later life.

Two limits are worth stating. The study covered adults of European ancestry in middle and older age, and its cognitive measures were brief composites that fall short of a full IQ battery. Within those limits, it is the strongest evidence available, and it points to no lasting effect of habitual coffee on cognitive ability.

People often ask whether they should drink coffee before taking an IQ test. The honest answer is that it should make little difference to a fair estimate of your ability. If you drink coffee every morning, skipping it on test day may leave you slightly slower and sleepier than normal, and having your usual amount simply keeps you at your normal level. If you rarely consume caffeine, a large dose may make you jittery without improving your reasoning, which is what the Rogers study found in low consumers.

A good night's sleep matters more than any stimulant, as covered in our article on how sleep affects IQ and cognitive performance, and the broader routine for test day is set out in our guide on how to prepare for an IQ test. The general principle holds for most test-day factors, including the ones discussed in our article on the impact of motivation on IQ: conditions that leave you tired or ill can pull a score down, while nothing taken on the morning of a test can push it meaningfully above your typical level.

No. Caffeine speeds reaction time and increases alertness, but controlled studies show little effect on reasoning, and a large genetic study found no long-term effect of coffee drinking on cognitive ability.

If you normally drink coffee, having your usual amount avoids withdrawal-related sluggishness. Extra caffeine is unlikely to raise your score and may make you jittery.

Some observational studies find coffee drinkers score slightly better on certain tests, but the results are inconsistent and confounded by lifestyle and social factors. Genetic studies that avoid those confounds find no causal effect.

Yes, mildly. People who skip their usual caffeine become sleepier and slower on reaction-time tasks, which is why much of caffeine's apparent benefit in studies is the reversal of withdrawal.

The evidence is observational and mixed: a French cohort of 1,083 mother-child pairs linked each additional 100 mg of daily caffeine to about 0.9 fewer IQ points at age 5.5, while a US study of 2,197 pairs found no meaningful association. Pregnant people with questions about caffeine should ask their obstetrician or midwife.

Caffeine is a useful stimulant and a poor intelligence booster. It makes people faster and more alert, especially when they are short of sleep or in withdrawal, and it does very little for the reasoning and problem solving that IQ tests measure. Over the long run, the best genetic evidence shows that a coffee habit neither raises nor lowers cognitive ability. If you want an accurate picture of your reasoning ability, rested and on your normal routine, take a full-length online IQ test.

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2. Nehlig, A. (2010). Is caffeine a cognitive enhancer? Journal of Alzheimer's Disease, 20(Suppl. 1), S85-S94. [doi.org/10.3233/JAD-2010-091315](. doi.org

3. Kamimori, G. H., McLellan, T. M., Tate, C. M., Voss, D. M., Niro, P., & Lieberman, H. R. (2015). Caffeine improves reaction time, vigilance and logical reasoning during extended periods with restricted opportunities for sleep. Psychopharmacology, 232(12), 2031-2042. [doi.org/10.1007/s00213-014-3834-5](. doi.org

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7. Zhou, A., Taylor, A. E., Karhunen, V., Zhan, Y., Rovio, S. P., Lahti, J., Sjögren, P., Byberg, L., Lyall, D. M., Auvinen, J., Lehtimäki, T., Kähönen, M., Hutri-Kähönen, N., Perälä, M. M., Michaëlsson, K., Mahajan, A., Lind, L., Power, C., Eriksson, J. G., Raitakari, O. T., Hägg, S., Pedersen, N. L., Veijola, J., Järvelin, M.-R., Munafò, M. R., Ingelsson, E., Llewellyn, D. J., & Hyppönen, E. (2018). Habitual coffee consumption and cognitive function: A Mendelian randomization meta-analysis in up to 415,530 participants. Scientific Reports, 8, 7526. [doi.org/10.1038/s41598-018-25919-2](. doi.org

8. Galéra, C., Bernard, J. Y., van der Waerden, J., Bouvard, M. P., Lioret, S., Forhan, A., De Agostini, M., Melchior, M., Heude, B., & the EDEN Mother-Child Cohort Study Group. (2016). Prenatal caffeine exposure and child IQ at age 5.5 years: The EDEN mother-child cohort. Biological Psychiatry, 80(9), 720-726. [doi.org/10.1016/j.biopsych.2015.08.034](. doi.org

9. Klebanoff, M. A., & Keim, S. A. (2015). Maternal caffeine intake during pregnancy and child cognition and behavior at 4 and 7 years of age. American Journal of Epidemiology, 182(12), 1023-1032. [doi.org/10.1093/aje/kwv136](. doi.org

Hero image: Espresso Coffee 01 by Jubair1985, CC0. Via Wikimedia Commons.