Caffeine is a natural alkaloid present in more than 60 plants 23. Methylxanthine caffeine is one of the most consumed stimulants in the world. It is a mild central nervous system stimulant, a vasodilator and a diuretic 22. Caffeine is present in a wide range of dietary products such as coffee, tea, coca, chocolate bars, soft drinks and energy drinks. Additionally, a number of prescription and over-the-counter (OTC) medications, used for headache, cold, allergy, and pain and alert medications, are often combined with caffeine. Some examples of these drugs are as follows: No-Doz, No-Doz Plus and Cafergot 24, 25. Say no to plagiarism. Get a tailor-made essay on "Why Violent Video Games Shouldn't Be Banned"? Get an original essay After oral ingestion, caffeine is rapidly and almost completely absorbed from the gastrointestinal tract and reaches peak plasma concentration approximately 30 to 60 minutes after consumption. The volume of distribution is 0.6 L/Kg and 36% is protein bound. It passes through the blood brain barrier and all biological membranes. It is metabolized in the liver by the cytochrome P450 (CYP) system to dimethylxanthine stimulants, theobromine, and theophylline. The elimination half-life is 4.5 hours in healthy non-smoking adults. Mechanism of action Adenosine A1 and A2A receptors are present in the basal ganglia. The basal ganglia are a group of structures that aid in various motor controls. As shown in Table 1, adenosine A1 receptors are present in all areas of the brain while A2A receptors are found more in dopamine-rich regions of the brain. There is evidence that A2A receptors interact with the dopamine system, which is involved in reward and arousal effects. 27. Caffeine acts as an antagonist on both types of receptors. The overall psychostimulant properties of caffeine in the brain are mediated by its ability to interact with neurotransmission in different brain regions. Caffeine has been shown to specifically affect a group of projection neurons located in the striatum, which is the main recipient area of ​​the basal ganglia 29. Thus, caffeine blocks the inhibitory neurotransmitter adenosine, inhibits phosphodiesterase, and increases adenosine monophosphate cyclic intracellular (cAMP) 28. At low concentration, blocks adenosine receptors, however, at higher concentrations, inhibits phosphodiesterase and calcium mobilization 27. Physiological effects Please note: this is just a sample. Get a custom paper from our expert writers now. Get Custom EssayIn a literature review by Glade, it was found that caffeine in moderate amounts increases energy, decreases fatigue, improves physical, motor and cognitive performance, increases alertness, decreases mental fatigue, increases precision of the reaction and improves cognitive functioning skills and neuromuscular coordination 30. The author did not specify the effective dose in the study. However, the medical website Rx-list mentioned that doses of 100-200 mg of caffeine can increase alertness, relieve drowsiness and improve thinking and at doses of 250-700 mg per day, caffeine can cause anxiety, insomnia , nervousness, hypertension and insomnia 31. Furthermore, an article by Pohler mentions that caffeine, if taken in excessive quantities, can have effects on all organs of the body (Table 2) 32.