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Caffeine is a central nervous system (CNS) stimulant of the methylxanthine class and is the most commonly consumed psychoactive substance globally. [9] [10] It is mainly used for its eugeroic (wakefulness promoting), ergogenic (physical performance-enhancing), or nootropic (cognitive-enhancing) properties.
Caffeine dependence can cause a host of physiological effects if caffeine consumption is not maintained. Withdrawal symptoms may include headaches, fatigue, difficulty concentrating, lack of motivation, mood swings, nausea, insomnia, dizziness, cardiac issues, hypertension, anxiety, backaches, and joint pain; these can range in severity from mild to severe. [18]
However, at higher doses, these stimulatory effects can become excessive and lead to a wide range of unpleasant symptoms including a dysphoric physical and mental state that is labeled caffeinism and is also known colloquially as "coffee nerves" or "caffeine jitters."
The U.S. Food and Drug Administration (FDA) says that most people can tolerate up to 400 milligrams of coffee a day—that lines up to between two and three 12 oz cups of the good stuff each day ...
The 36 others were simply given caffeine diluted in hot water — no coffee — and underwent the same types of MRI scans before and after they consumed the beverage.
The physical effects of caffeine include lowered sensations of pain, less perceived effort, and increased muscle strength and endurance. However, at doses above ~400 mg, both cognitive and physical performance begins to worsen and symptoms of anxiety increase. [ 12 ]
The intensity of caffeine’s effects can depend on the time of day you consume it because of the body’s circadian rhythm, or the natural body clock that signals when it’s time to sleep and ...
The health effects of coffee include various possible health benefits and health risks. [ 1 ] A 2017 umbrella review of meta-analyses found that drinking coffee is generally safe within usual levels of intake and is more likely to improve health outcomes than to cause harm at doses of 3 or 4 cups of coffee daily.