Mental alertness and performanceĬaffeine’s stimulant effect has been shown to enhance mental alertness and performance, particularly in people who don’t regularly consume it ( 15). The participants who received caffeine continued to experience greater performance benefits compared with the placebo after the 15 days, but the progressive decline in performance thereafter suggests a gradual but partial tolerance to caffeine’s effects. In one 20-day study, 11 people with light caffeine use consumed a pill containing 1.4 mg of caffeine per pound (3 mg per kg) of body weight or a placebo daily ( 14).Ĭompared with the placebo, the daily intake of caffeine increased cycling power during 2 exercise tests by 4–5% for the first 15 days, but then the performance effect decreased. Yet, these performance benefits may decrease with regular caffeine consumption. Several studies have demonstrated that caffeine can improve muscle strength and power, as well as delay fatigue with exercise ( 12, 13).

Research suggests that caffeine does not lead to greater increases in blood pressure in people with high blood pressure who regularly consume caffeine ( 11). Caffeine did not affect heart rate ( 10). This amount represents about 200 mg of caffeine, or two 8-ounce (240-mL) cups of coffee for a 150-pound (68-kg) person.Ĭompared with the placebo, caffeine significantly increased blood pressure, but the effect disappeared after 8 days. In one 20-day study, 11 people with light caffeine use consumed a pill containing 1.4 mg of caffeine per pound (3 mg per kg) of body weight per day or a placebo ( 10). Blood pressure and heart rateĬaffeine increases blood pressure in the short term, but a tolerance to this effect develops quickly with regular intake ( 8, 9). Regularly consuming caffeine increases the number of adenosine receptors, decreasing caffeine’s effects.Ĭaffeine tolerance occurs when the effects of caffeine decrease over time with regular consumption.Ī tolerance to caffeine’s effects has been demonstrated on blood pressure, exercise performance, and mental alertness and performance. summaryĬaffeine increases alertness and decreases fatigue by blocking adenosine from binding to its receptor. However, according to a seminal study from the 1980s, regularly consuming caffeine increases your body’s production of adenosine receptors and therefore the likelihood of adenosine binding to those receptors ( 7).Ĭonsequently, this decreases caffeine’s effects, causing you to become tolerant over time ( 7). The stimulating effects of caffeine occur within 30–60 minutes of consuming the substance and last for 3–5 hours, on average ( 3, 6).

One study showed that a high caffeine dose can block up to 50% of adenosine receptors in the brain ( 5). Caffeine mainly works by blocking your brain’s adenosine receptors, which play a role in sleep, arousal, and cognition ( 1).Ī molecule called adenosine usually binds to these receptors, inhibiting the release of brain chemicals like dopamine that increase arousal and promote wakefulness ( 2).īy blocking adenosine from binding to its receptor, caffeine increases the release of these stimulating brain chemicals that decrease fatigue and increase alertness ( 3, 4).

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