Effects of Caffeine on Cognition and Mood



Understanding the implications of caffeine use is essential for clinicians. Just like many anti-depressants, caffeine molecules will bypass the blood-brain barrier and affect cognition and mood. Since over 90% of North Americans consume caffeine daily, as professionals, it is vital to intimately understand the effects of caffeine on cognition and mood.

To illustrate the importance of understanding caffeine, consider a patient that comes to you and says he thinks he needs something to manage what he describes as ADHD. He describes his symptoms as his being unable to concentrate and jitteryness. One might look at the symptoms, diagnose ADHD, and assume medication is required. This might be a big mistake if his problems could be fixed simply by reducing his caffeine intake.


On the other hand, caffeine is one of the safest stimulants when used properly. Many studies have shown increases in alertness, mood, and performance after consuming caffeine.


Physiological Effects of Caffeine

Caffeine is typically found in plants, where it acts as a pesticide to ward off insects feeding on the plants. Caffeine is a xanthine alkaloid that affects the central nervous system (CNS) and acts as a psycho-stimulant. Many of the physiological effects of caffeine can be seen by observing an individual's behavior. The observed effects of caffeine depend on the dose consumed. For individuals consuming caffeine in a normal manner, the most common physiological changes are increased arousal, nervousness, an exaggerated startle response, and an elevated heart rate. Common effects of strong doses of caffeine intake include reduced eye contact, hyperactivity, anxiety, and bursts of energy or mania.

Caffeine is commonly prescribed in neonatal intensive care, where it is used to treat breathing problems in newborns who are born prematurely.

Regular caffeine use causes tolerance and dependency, similar to other stimulants. It can be very hard to quit caffeine, and many people remain addicted for their entire lives.

Caffeine's Effects By Dose

After dosing, the onset of the effects of caffeine are felt between five and ten minutes and they last from one to five hours. Aftereffects can be felt for up to 24 hours.

Threshold – 10-20 mg. A threshold dose of caffeine is non-addictive and generally considered safe by most doctors.

Common – 50-150 mg. At this level, caffeine addiction begins. One should avoid exceeding this dosage.

Strong – 150-400 mg. A strong dose of caffeine is typically accompanied by the early signs of caffeine intoxication, including jitteriness and an increased heart rate. Other symptoms include irritability, restlessness, and an increased risk of heart disease.

Heavy – 400-750 mg. A heavy dose of caffeine has been shown to cause stomach and gastrointestinal problems. It can cause tension, hyperactivity, insomnia, excitement, high irritability, moodiness, personality disorders, irregular heartbeat. Daily use can increase your risk of heart disease.

Severe Intoxication – 750+ mg. This can result in anxiety, tremors, seizures, vomiting, nausea, tachycardia, and hypotension.

Lethal – 3-20 grams oral. Requires Emergency Room attention.


Caffeine Content of Common Beverages

Energy drinks – All are in excess of 100 mg per 12oz.

Pepsi One – 55 mg/12oz

Mountain Dew – 55 mg/12oz

Surge – 52.5 mg/12oz

Nestea Earl Grey – 50mg/12oz

Tab – 46.8mg/12oz

Coca-Cola, Diet – 46mg/12oz

Shasta Cola – 44.4mg/12oz

RC Cola – 43.2mg/12oz

Dr. Pepper – 41mg/12oz

Mr. Pibb – 40.8mg/12oz

Pepsi – 38.4mg/12oz

Coca-Cola – 34mg/12oz

Snapple – 31.5mg/12oz

Coffee – 150mg/12oz

Tea – 140mg/12oz


Psychiatric Classification of Caffeine-Related Disorders

In Psychiatry, caffeine use is commonly associated with several psychiatric syndromes: caffeine intoxication, withdrawal, dependence, caffeine-induced anxiety disorder, and caffeine-induced sleep disorder. In the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV-TR), we find some of the dangers of caffeine dependency. The DSM-IV-TR includes four caffeine-related disorders:


Caffeine Intoxication

Caffeine intoxication is an acute disorder, brought on by over-consumption of caffeine in a short period. Five or more of the following symptoms are sufficient to diagnose caffeine intoxication: restlessness, nervousness, excitement, insomnia, flushed face, diuresis, gastrointestinal disturbance, muscle twitching, rambling flow of thought and speech, tachycardia, cardiac arrhythmia, periods of inexhaustibility, and psychomotor agitation. 

For a person with no caffeine tolerance, caffeine intoxication will occur with consumption over 250 mg. Not much is known about what subset of the population is most at risk of caffeine intoxication. Caffeine intoxication can occur in someone who uses caffeine regularly, but is most likely in someone who has consumed caffeine in excess of their typical dose.

Caffeine-Induced Anxiety Disorder

Caffeine-Induced Anxiety Disorder typically presents with symptoms similar to panic attacks or generalized anxiety. Caffeine-induced anxiety disorder can be diagnosed when there is evidence from the history, physical examination, or laboratory findings suggesting that anxiety developed within one month of caffeine intoxication. Particularly important to this diagnosis is a predomination of anxiety that cannot be accounted for by a pre-existing anxiety disorder.


Caffeine-Induced Sleep Disorder

Caffeine-induced sleep disorder is a severe disturbance of sleep such that clinical attention is warranted. Evidence should point to the sleep disturbance being a physiological consequence of caffeine consumption, and not be better accounted for by another mental disorder.


Caffeine-Related Disorder Not Otherwise Specified

Any caffeine disorder not otherwise listed could be considered a Not Otherwise Specified disorder if it significantly impairs social, occupational, or other important areas of functioning and can be shown to be directly related to consumption of caffeine.


Caffeine Dependence

Substance dependence is characterized by cognitive, physiological, and behavioral symptoms. Dependence involves the continued use of a substance despite evidence that its use is causing problems. Caffeine Dependence is recognized by the World Health Organization as a type of substance dependence, but it is not presently included in the DSM-IV. More research needs to be done on the applicability of the criteria of substance dependence to caffeine dependency. Meanwhile, counselors should provide therapeutic assistance to those patients who feel that their caffeine use is problematic.


Psychiatric Impact of Caffeine on Abnormal Groups

Anxiety Disorder – Caffeine has shown to cause anxiety in many controlled studies. Some people just feel more jittery, but it can cause an episode in those with anxiety disorders or those prone to panic attacks. According to Bruce (1989), " ....caffeine is routinely used to induce panic attacks in clinical experiments. When given caffeine doses of the equivalent of that in 4 - 5 cups of coffee, nearly half of panic disorder patients, experienced a reaction that was indistinguishable from a spontaneous panic attack." Studies show that high doses of caffeine (above 200 mg per day) increase anxiety in healthy populations. Highly anxious individuals are especially sensitive to these effects.

Social Anxiety – Studies have shown an immediate impact of the reduction of caffeine on reducing a patient's anxiety. In borderline cases, removal of an environmental trigger like caffeine is one of the easiest steps that can be taken towards rehabilitation.

Diabetics – Caffeine can raise the level of sugar in the blood.

Depression – In small amounts, studies have found that caffeine may help depression. For some, depression is due to a chemical imbalance of dopamine and serotonin. Caffeine causes neurotransmitters to excrete these two chemicals. In large amounts, caffeine also depletes your body of Vitamin B6, which is a known cause of depression and anxiety, so in these patients, a simple B6 supplement might be in order.

Bipolar Disorder – Caffeine toxicity may actually be mistaken for bipolar disorder. Symptoms of both caffeine and bipolar disorder include mood swings, impulsiveness, and chattiness.

Attention Deficit Disorder – Caffeine toxicity can mimic ADD and ADHD. It is rumored that as many as ten percent of ADHD cases may be misdiagnosed and attributable to caffeine-related disorders.

Insomniacs – Caffeine can disrupt sleep cycles. A disrupted sleep cycle leads to exhaustion during the day. This can lead to an increased intake of caffeine which will further disrupt sleep cycles.

Prone to Arrhythmia – Caffeine will increase a patient's heart rate and blood pressure. This can be life-threatening when combined with a propensity for heart problems.

Prone to Stress – Caffeine increases the secretion of hormones related to stress, like adrenaline. Even a small amount of caffeine can be a problem for those sensitive to its effects.


Treatment for Caffeine-related Disorders

Caffeine Intoxication

Caffeine intoxication is rarely fatal. Extreme overdose (in excess of 3-5 grams, roughly fifty cups of coffee) can be a lethal dose and should be treated in an Emergency Room. Extreme overdose is very unlikely through consumption of coffee, but with the prevalence of caffeine tablets and energy drinks, it has occurred.


Caffeine-Induced Anxiety Disorder

Administration of theanin has been shown to greatly reduce caffeine-induced anxiety. A patient who has ingested enough caffeine to require clinical attention should be slowly weened from caffeine. Caffeine-induced anxiety disorder can present similarly to obsessive-compulsive disorder, phobia, schizophrenia, panic attacks, or generalized anxiety. Many medical professionals have concluded that, because caffeine-related disorders may be as common as ten-percent of the population, many of these disorders may be misdiagnosed and treated with unnecessary medication.


Caffeine-Induced Sleep Disorder

An individual who regularly ingests enough caffeine to require clinical attention should be slowly weened from caffeine. Many times, sleep disorders are treated with sleeping pills, but the treatment for caffeine psychosis is simply to stop further caffeine intake.


Caffeine Dependence

Caffeine withdrawal is common and rarely dangerous. Withdrawal usually starts between 12 and 48 hours of the last intake of caffeine and lasts between two and nine days. The most frequent symptom of caffeine withdrawal is moderate to severe headaches, but other common symptoms include sleepiness, nausea, vomiting, muscle pain, or stiffness. Advise the individual about the expected symptoms of withdrawal and the duration of symptoms. If discomfort persists beyond two weeks, this may be due to a different disorder. Be aware that treatment may unmask other conditions.


Reducing Your Caffeine Intake - Caffeine Fading

Most people report success by reducing their caffeine intake by a half cup of coffee each day. The best way to cut down your use of coffee is to consume beverages regularly for one week and keep a journal of all the times and amounts of caffeine intake. Then, over the next week, work to reduce daily intake by about 50 mg per day.


Adolescent Use of Caffeine

It is common to see children and teenagers downing “big gulp” and super-sized sodas. The caffeine content of a “big gulp” 32 oz. soda is roughly the same as three cups of coffee. The prevalence of soft drink consumption among children and adolescents has brought caffeine-related disorders to the forefront of counseling and therapy. The energy drink market keeps expanding to meet the public demand of high-caffeine drinks. Some people even drink them with meals. Advertising for many energy drinks is targeted specifically at teens. School districts are bending over backwards to get funding from soda companies. In exchange, they're putting the soda company's logo on everything from vending machines to mousepads in the computer lab.

A Psychiatrist at the National Institute of Mental Health found that more than one-third of students who regularly guzzled high doses of caffeine met the criteria for diagnosis of attention deficit disorder with hyperactivity.

According to Roland Griffiths of Johns Hopkins Medical Institutions, "The caffeine content of energy drinks varies over a 10-fold range, with some containing the equivalent of 14 cans of Coca-Cola, yet the caffeine amounts are unlabeled and few include warnings about potential health risks of caffeine intoxication."

A physician wrote the following case study in a New York Times article: Recently, one of my colleagues, a pediatric gastroenterologist, told me about a teenage boy who had come to see him because of severe stomach pain he'd had for about two months. The boy had been referred by his primary care doctor, who had evaluated him for several possible causes, including infections and ulcers. That doctor had also recommended or prescribed a variety of medications to relieve the pain, but to no avail.

The specialist performed an endoscopy, in which a camera is inserted into a patient's esophagus and down into the stomach and upper part of the small intestine.The findings were impressive: severe inflammation, bleeding and ulcerations in a part of the small intestine called the duodenum, the portion of the intestine closest to the stomach.


When the medical team's members went back and got further history, they learned that the teen had been drinking several Redline energy drinks a day.

As a teenager, energy drinks can really tear up your guts. In a study of over 250 cases of caffeine intoxication, the average age for hospitalization was 21.


So what are we to tell concerned parents to do? Encourage your child to drink water. Purchase 100% fruit juice rather than soda. Teach your children about the dangerous effects of caffeine when consumed regularly or in large amounts.


Effects on Learning and Memory

Some physicians argue that caffeine has nootropic effects. In a study of rats, dendrite formation grew by 33% after the administration of caffeine. Another study showed that human subjects had frontal lobe activation after 100mg administration of caffeine. A contradictory study showed that caffeine could impair short-term memory when the range of information to be recalled is broad. The results of these studies suggest that the use of caffeine can aid short-term recall and increase cognitive performance during focused thought but reduce cognitive performance in broadly-ranged thinking tasks.



A growing body of evidence shows that caffeine can have beneficial effects on attentional processes. Across a wide number of studies, increased caffeine intake elevated mood and decreased drowsiness.

However, caffeine dependency can be a harmful condition. This is exacerbated by the fact that diagnosis of caffeine-related disorders can be difficult. Any complaint of sleep difficulty should include an assessment of beverage consumption. Beverage caffeine is so common in everyday life that its consumption is routinely neglected in clinical diagnoses.

Clinicians should be wary of the impact of caffeine on problem groups, including those with ADD, Bipolar Disorder, Depression, Diabetes, Social or General Anxiety, Insomniacs, or those prone to stress, as caffeine can exacerbate these problems.

It is particularly important for therapists to be able to identify caffeine-related disorders and properly diagnose them. Before medicating for a disorder, it might be easier to treat the patient by encouraging them to lower their caffeine intake.


Current Research

Brunyé, T. T., Mahoney, C. R., Lieberman, H. R., & Taylor, H. A. (2010). Caffeine modulates  attention network function. Brain and Cognition, 72(2), 181-188.

This study investigated the effects of caffeine on visual attention. Caffeine improved alerting and executive control function.  Results of this study demonstrate that caffeine has differential effects on visual attention networks as a function of dose. Additionally, on a self-reported mood state questionnaire, there were significant increases in participants' ratings of how Lively, Peppy, and Jittery they felt.

Fredholm, B. B., Bättig, K., Holmén, J., Nehlig, A., & Zvartau, E. E. (1999). Actions of Caffeine in the Brain with Special Reference to Factors That Contribute to Its Widespread Use. Pharmacological Reviews, 51(1), 83-133. 

This article has an extensive literature review that cites many studies from the 70s through 90s that are not available online. According to the article, lower doses of caffeine (20-200mg) are reliably associated with "positive" subjective effects. Subjects report that they feel energetic, imaginative, efficient, self-confident, and alert (Griffiths et al., 1990). School children consuming more than 50mg of caffeine per day report higher wakefulness than a control group consuming less than 10mg per day (Goldstein and Wallace, 1997). Caffeine can be more effective on improving cognition and mood in subjects that are less alert than usual. Subjects with upper respiratory tract illness felt more alert after consuming caffeine and performed better on a reaction time test (Smith et al., 1997). Outpatients undergoing treatment for psychiatric disorders who consumed more than 1000 mg of caffeine per day had symptoms of generalized anxiety (Greden 1974); however, caffeine's impact on the anxiety levels of a normal population has been disputed (Eaton and McLeod, 1984). It would seem that high doses of caffeine can induce a state of anxiety in certain individuals, but not in others.

Haskell, C. F., Kennedy, D. O., Milne, A. L., Wesnes, K. A., & Scholey, A. B. (2008). The effects of l-theanine, caffeine and their combination on cognition and mood. Biological Psychology, 77(2), 113-122.

Numerous studies have been carried out on the effects of caffeine, but this one was particularly interested in the effects of tea containing caffeine. Tea reduces cortisol levels in response to stress, while caffeine increases cortisol levels. On self-assessment of mood, L-theanine was synergistic with caffeine in increasing alertness, reducing tiredness, and reducing headaches.

Horne, J. A., & Reyner, L. A. (1996). Counteracting driver sleepiness: Effects of napping, caffeine, and placebo. Psychophysiology, 33(3), 306-309. 

In this study of driving while tired, caffeine significantly reduced driving impairment, subjective sleepiness, and electroencephalographic (EEG) activity indicating drowsiness. 

James, J., & Rogers, P. (2005). Effects of caffeine on performance and mood: withdrawal reversal is the most plausible explanation. Psychopharmacology, 182(1), 1-8. 

This article argues that other studies into caffeine's effect on cognition and mood do not properly control for withdrawal effects. James & Rogers' results indicate that there is little evidence of caffeine having beneficial effects on performance or mood under conditions of long-term caffeine use vs abstinence. According to this research, acute effects may occur following initial use, but tolerance develops in the context of habitual use of the drug. They argue that while almost all studies perceive to show psycho-stimulant effects, almost all are wholly attributable to the reversal of adverse withdrawal effects associated with abstinence from the drug.

Kilpeläinen, A. A., Huttunen, K. H., Lohi, J. J., & Lyytinen, H. (2010). Effect of Caffeine on Vigilance and Cognitive Performance During Extended Wakefulness. The International Journal of Aviation Psychology, 20(2), 144 - 159. 

In this study, participants who received caffeine showed overconfidence, frequently reporting increased mood and motivation, despite impaired performance in objective tests.

Leathwood, P. D., & Pollet, P. (1982). Diet-induced mood changes in normal populations. J Psychiatr Res, 17(2), 147-154. 

Caffeine significantly increased self-reported scores on the following scales: wakefulness, vigour, clarity of mind, energy, feeling full of ideas, feeling full of go, and feeling efficient.


Lieberman, H., Tharion, W., Shukitt-Hale, B., Speckman, K., & Tulley, R. (2002). Effects of caffeine, sleep loss, and stress on cognitive performance and mood during U.S. Navy SEAL training. Psychopharmacology, 164(3), 250-261. 

Contrary to the results in the Kilpeläinen study, participants here did have significant improvements in both subjective and objective criteria.

Lieberman, H. R., Wurtman, R. J., Emde, G. G., Roberts, C., & Coviella, I. L. G. (1987). The effects of low doses of caffeine on human performance and mood. Psychopharmacology, 92(3), 308-312. 

In this study, caffeine was found to have a positive effect on vigilance and visual reaction time, even in doses as small as 32mg. This study did not observe any adverse behavioral effects, increased anxiety, or impaired motor performance.

Loke, W. H. (1990). Effects of repeated caffeine administration on cognition and mood. Human Psychopharmacology: Clinical and Experimental, 5(4), 339-348. 

This study did not show any increase in cognitive performance with any dose under 600 mg. A mood assessment suggests that individuals were sensitive to the effects of caffeine but the effects did not interfere with cognitive performance.

Peeling, P., & Dawson, B. (2007). Influence of caffeine ingestion on perceived mood states, concentration, and arousal levels during a 75-min university lecture. Advan. Physiol. Edu., 31(4), 332-335.

After caffeine consumption, students perceived themselves to be significantly more awake, clear minded, energetic, alert, anxious, and better able to concentrate.

Rebecca, L. O., Mary, D. O., Darmendra, R., Michael, D. K., & Rebecca, L. (2006). High caffeine intake in adolescents: associations with difficulty sleeping and feeling tired in the morning. The Journal of adolescent health : official publication of the Society for Adolescent Medicine, 38(4), 451-453. 

Simply found that adolescents with a higher intake of caffeine tended to have difficulty sleeping and felt tired in the morning.

Smit, H. J., & Rogers, P. J. (2000). Effects of low doses of caffeine on cognitive performance, mood and thirst in low and higher caffeine consumers. Psychopharmacology, 152(2), 167-173. 

Effects confirmed a psychostimulant effect with all doses of the treatment.

Smith, A. (2002). Effects of caffeine on human behaviour. Food and Chemical Toxicology, 40, 1243-1255.

Regular caffeine use appears to be beneficial. In contrast, there are reports that have demonstrated negative effects when given to sensitive groups.

Smith, A. (2009). Effects of caffeine in chewing gum on mood and attention. Human Psychopharmacology: Clinical and Experimental, 24(3), 239-247. 

Compared the effects of caffeinated gum, placebo gum, and no gum conditions on mood and attention. Caffeinated gum was associated with better performance and positive mood on tasks that required sustained attention. Chewing placebo gum also caused a more positive mood.

Strain, E. C., Mumford, G. K., Silverman, K., & Griffiths, R. R. (1994). Caffeine Dependence Syndrome: Evidence From Case Histories and Experimental Evaluations. JAMA, 272(13), 1043-1048.

Of ninety-nine subjects who self-identified as being psychologically or physically dependent on caffeine, sixteen were identified as having a diagnosis of caffeine dependence. Median daily caffeine intake for the group was 357 mg. These results suggest that caffeine exhibits many of the same characteristics of a typical psychoactive dependence.