Caffeine: Neurophysiological Effects on Humans


  • Finland is the world’s top coffee consuming nations
  • Caffeine is the most widely used psychoactive stimulant globally
  • It is also known as an “ancient wonder drug”



Caffeine which is known to be a psychoactive stimulant is the most consumed content globally. It is popular across all age groups. Caffeine is found in the coffee bean, cocoa bean, the kola nut and tea leaves. Caffeine abuse, is an issue which is on the rise due to a rise in energy drink consumption. As aggressive branding and marketing strategies implemented by energy drink manufacturers and the awareness regarding the consequences of high use of caffeine being low, caffeine abuse has become an issue of concern all over the world.  As the consumption of caffeine is so common, it is important to know the impact of caffeine on the body, as it can affect endocrine, cardio-respiratory and most significantly neurological systems. Deleterious effects can be seen due over consumption of caffeine levels rising. This review aims to shed light on the neuropsychological and neurophysiological impact of caffeine and its effects on the human health.

People today need energy and enthusiasm to complete their demanding lifestyles and schedules. Often, they need some sort of boosters. Caffeine is a natural chemical. It is called the “ancient wonder drug” as it can rejuvenate an exhausted individual. Caffeine was found in the coffee beans in Arabia, the kola nut in West Africa, the cocoa bean in Mexico and the tea leaf in China. Products that contain caffeine are consumed globally by so many people, that caffeine abuse may go unnoticed. According to research, caffeine is the world’s most extensively consumed content, with almost 60% of American adults consuming an average of three cups of coffee daily. Caffeine does occur naturally incoffee and tea, but now it is being used as an additive in energy drinks, chocolates, soft drinks bottled water and medication all over the world.

Caffeine Consumption

Caffeine is now being added to food products such as chocolates, different types of chips and bottled water, which confirms its popularity which is on a rise. Red Bull was launched in 1987, the energy drink market has evolved since this brand came into existence. Many other brands in this sector followed suit by producing caffeine content drinks. According to reports, there has been an increase in caffeine-intoxication since 1980s, as caffeine abuse cases reported in the United States from 2002 to 2004 have been gradually rising. So this is an alarming situation of caffeine dependence and withdrawal symptoms.

According to statistics in North America and Europe, ninety percent of adults consume caffeine with an average intake of 227 mg on a daily basis.  South African Food Based Dietary According to the guidelines stated by South African Food Based Dietary, recommendations, that adults should not consume more than four cups of coffee per day or eight cups of tea per day, which is in sync with the US Food and Drug Administration recommendation where a moderate daily dose being 300 mg and below. The ideal quantity may be five 500 to 1800 mg. According to North American and European statistics the top three sources of caffeine are coffee (70%), energy drinks (16%), and tea (12%) in the United States.

As compared to instant coffee brewed coffee has almost three times the amount of caffeine. Energy drinks have twice the amount of caffeine compared to cold drinks. In the wake of a rise in energy drinks and coffee consumption, it is very crucial to analyze the hazards of caffeine as a content.

Biochemical Characteristics

The chemical structure of caffeine is 1, 3, 7 proportions of trimethylxanthine. Methylxanthine has a similar structure to adenosine, purines, uric acid and xanthine. Caffeine is found naturally in various plants, cherries, kola nuts and cocoa beans as it might protect plants by acting as an anti-herbivory and allelopathic agent. The gastrointestinal tract quickly absorbs the caffeine in human body. Caffeine which is present in coffee is absorbed much rapidly as compared to cold drink caffeine. This can happen as the temperature of the beverage being low which may decrease the blood flow rate within the intestines, phosphoric acid in cold drinks decreases gastric emptying. Absorption rate could increase according to the caffeine dose, sugar in cold drinks could hinder gastric emptying of caffeine and delay absorption. As a matter of fact, 99% of the orally ingested chemical is absorbed in forty five minutes by the body. Caffeine runs throughout the body getting into biological membranes, the blood brain barrier and placenta but it does not stagnate in the organ tissues. Caffeine and its primary metabolic elements, paraxanthine, theobromine and theophylline are present in all body fluids. Paraxanthine metabolites found in urine decrease less rapidly than caffeine and are further metabolized through two independent reactions. Theobromine is the largest part of caffeine metabolites, with only 50% passed out through urine.

Respiratory and Cardiovascular Effects

Caffeine has various cardiovascular effects such as regulation of circulating catecholamines. Endothelium dependent vasodilatation and arterial stiffness also result in increase of systolic and diastolic blood pressure. The prime effect dependent on the plasma caffeine value is the increased respiration rate.

Endocrine and Metabolic Effects

Circulation of catecholamine levels is enhanced by insulin. There is an increase in the basic metabolic process as it becomes faster due to this process.

Gastrointestinal and Urinary Effects

Caffeine is very much beneficial for the small intestine as it helps in secretion of sodium and water. According to medical perspective caffeine may promote apoptosis in UVB-damaged cells, to disaffect adenosine receptors for blood vessel contraction and even works as a psychoactive drug for treating Parkinson’s disease. So caffeine does have potential use in the medical field.

Caffeine Benefits for the Human Body

A research on animals, uses caffeine doses that are hundred to thousand times higher than those used for humans. Therefore, relating the results of precise caffeine effects to humans becomes difficult. Secondly, some studies investigate pure caffeine, while others experiment, using coffee, without analyzing other components in coffee and their potential effects. But in spite of these limitations, extensive research on caffeine has been carried out and has provided detailed information regarding the effects of caffeine.

Arousal and Fatigue

Arousal in humans can vary in terms of energy factors, task-related activation, the degree of knowledge a person possesses. With context to neuropsychology, an increase in arousal relates to a better ability to carry out a task. Caffeine effects and dopamine functions are interrelated, other neuromodulator systems should also be considered. According to reports caffeine increases the firing rates in mesopontine neurons, which are vital for arousal. These neurons are hindered by adenosine, giving a coupling mechanism that links arousal to caffeine. Caffeine can affect the attention system which alters the neural activity in cortical areas that may intensify the response ability of cells to specific stimulus features.  Many substantial studies show that caffeine consumption increases alertness and decreases fatigue. But only when consumed in moderate doses.

Perceptual Processing

Perception is a form of acquiring knowledge through senses, thought and experience.  Caffeine increased the ability to process degraded stimuli as the perceptual task required participants to discriminate between two targets per trial. One group which consumed caffeine showed significant difference in the perceptual task compared to those that did not receive caffeine. Another study was conducted for the effect of caffeine for sustained attention by subjects to work steadily for ten minutes in a self-timed task. The task consisted of a color selection and concentration. Subjects were given a moderate dose of 250 mg caffeine. The results showed an increase in arousal but no change in perceptual behavior. This shows that the overall effect of caffeine on is fairly inconsistent.

Motor Skills

Motor skill is one of the significant functions of the central nervous system. It is a process of increasing the temporal and spatial accuracy of hand eye movements through habits or practice. Motor skill has two important phases. An initial fast learning phase and a slow learning phase. In the initial stage, a great deal of performance enhancement is achievable within a few minutes. Precise knowledge of the movement is used to control and co-ordinate specific body action. The later phase learning is slow learning as less attention is needed to perform the task. The prefrontal cortex is responsible for guiding eye and head co-ordination. Dopamine is a neurotransmitter with inhibitory and excitatory effects. Caffeine increases behavior related to dopamine by inhibiting adenosine. Caffeine intake increased left frontal activation compared to the right side. As per this outcome suggesting that dopamine function could be linked to fatigue, with caffeine reducing fatigue. According to a study composed of 61 adults 18–39 years old that were given a motor task requiring them to finger tap a 4-1-3-2-4 sequence on a keyboard with the non-dominant hand. The caffeine group showed significantly impaired motor learning.

Learning and Memory

Learning is acquiring new information by the nervous system, resulting in behaviour changes or “analytical-specific perceptual skills”. Memory is the ability to store, process, and recall learnt information. Neurons in the hippocampus contribute to the formations of declarative memory units. These neurons can be trained to memorize perceptual images in a sequence. There is concern regarding strategies that can improve the elderly quality of life regarding the diminished cognitive and motor functions that occur with aging. In a study conducted where caffeine administered in adult mice prevented age-associated decline in recognition memory when evaluated 90 min after training (corresponding to short term memory). There is however, the possibility of anxiety being elicited, due to high caffeine doses.

Stress and Addiction

Stress is when the human body is not able to cope up to physical or emotional threats. The brain is the major component of interpreting and responding to potentially stressful events and determines what is stressful. It is also the central organ of the behavioral and physiological response to stressors and is also a target for the actions of stress hormones such as glucocorticoids. Studies show that during stress, there is an increase in caffeine consumption stimulating the central nervous system. So it is advised for individuals with hypertension to avoid caffeine during periods of stress as this further increases blood pressure. Chronic caffeine consumption causes sensitization of a specific subset of cannabinoid receptors in the striatum, consistent with the psychoactive properties of the compound. Caffeine is not suitable for patients with hypertension condition.


The huge fan following of caffeine has created an urge to discover the possible hazards to the human body. By studying the biochemical characteristics of caffeine, many novel perspectives have been discovered, one of them being, effects of caffeine absorption process in the body and metabolism. The neurophysiological benefits of caffeine could lead to deeper medical insights. Caffeine should be consumed in moderation for attaining benefits. The neurophysiological negative impacts of caffeine include anxiety, panic attacks and hallucinations. Caffeine may also damage learning and memory.  As caffeine is similar to other drugs like ethanol, heroin, morphine and most importantly cocaine. It shows most similarity to cocaine and reinforces cocaine-seeking behavior according to research. This similarity of caffeine can prove to be fatal as awareness needs to be created.

Energy drinks containing caffeine should be consumed in moderation as there are high chances of caffeine abuse especially by youngsters. Considering the neurophysiological implication of caffeine use, branding and marketing of energy drinks and caffeinated soft drinks should be restructured and executed accordingly. Caffeine addiction is also an issue of major concern. Other alternatives for boosting energy levels should be considered. Caffeine consumed in moderation will always prove beneficial for human health.