Caffeine is a stimulant found naturally in beverages like coffee and tea. It’s also added to others, such as energy drinks and soda.

Caffeine increases chemicals in your brain that improve mood, combat fatigue, and enhance focus.

For this reason, many people turn to their caffeine-containing beverage of choice to get their day started or pick themselves up from a mid-afternoon crash.

However, it’s thought that caffeine’s stimulating effects become less noticeable over time because your body becomes tolerant or less responsive to its effects.

This article explains how caffeine produces its stimulating effects and whether it’s possible to develop a caffeine tolerance.

Caffeine mainly works by blocking your brain’s adenosine receptors, which play a role in sleep, arousal, and cognition (1).

A molecule called adenosine usually binds to these receptors, inhibiting the release of brain chemicals like dopamine that increase arousal and promote wakefulness (2).

By blocking adenosine from binding to its receptor, caffeine increases the release of these stimulating brain chemicals that decrease fatigue and increase alertness (3, 4).

One study showed that a high caffeine dose can block up to 50% of adenosine receptors in the brain (5).

The stimulating effects of caffeine occur within 30–60 minutes of consuming the substance and last for 3–5 hours, on average (3, 6).

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).

Consequently, this decreases caffeine’s effects, causing you to become tolerant over time (7).


Caffeine increases alertness and decreases fatigue by blocking adenosine from binding to its receptor. Regularly consuming caffeine increases the number of adenosine receptors, decreasing caffeine’s effects.

Caffeine tolerance occurs when the effects of caffeine decrease over time with regular consumption.

A tolerance to caffeine’s effects has been demonstrated on blood pressure, exercise performance, and mental alertness and performance.

Blood pressure and heart rate

Caffeine increases blood pressure in the short term, but a tolerance to this effect develops quickly with regular intake (8, 9).

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).

This amount represents about 200 mg of caffeine, or two 8-ounce (240-mL) cups of coffee for a 150-pound (68-kg) person.

Compared with the placebo, caffeine significantly increased blood pressure, but the effect disappeared after 8 days. Caffeine did not affect heart rate (10).

Research suggests that caffeine does not lead to greater increases in blood pressure in people with high blood pressure who regularly consume caffeine (11).

Exercise performance

Several studies have demonstrated that caffeine can improve muscle strength and power, as well as delay fatigue with exercise (12, 13).

Yet, these performance benefits may decrease with regular caffeine consumption.

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).

Compared 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.

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.

Mental alertness and performance

Caffeine’s stimulant effect has been shown to enhance mental alertness and performance, particularly in people who don’t regularly consume it (15).

In regular caffeine consumers, the increase in mental alertness and performance that’s often reported is more related to a reversal of the symptoms of caffeine withdrawal rather than an enhancement above their normal state (16, 17).

You can develop a dependence on caffeine in as few as 3 days of use and from doses as low as 100 mg per day, which is the equivalent of an 8-ounce (240-mL) cup of coffee (18).

The symptoms of caffeine withdrawal include sleepiness, lack of concentration, and headache. They appear after 12–16 hours without caffeine and peak around 24–48 hours (19).


Regularly consuming caffeine can increase your tolerance to many of its effects, including those on blood pressure, exercise performance, and mental alertness and performance.

You can overcome a tolerance to caffeine’s effects by decreasing your caffeine intake or consuming it less often.

Consuming more caffeine than you normally do can also help you overcome your tolerance in the short term.

In one study, researchers examined the effects of caffeine on self-reported mood and cognition in 17 people who drank coffee daily (20).

The participants were instructed to either consume coffee like they normally do or abstain from it for 30 hours before receiving a pill containing 250 mg of caffeine or a placebo.

Compared with the placebo, caffeine improved the participants’ attention and memory even when they didn’t abstain from coffee, suggesting that among daily coffee drinkers, there may be some benefits to consuming more than normal (20).

In either case, it’s not recommended to continually increase your intake of caffeine in an attempt to experience greater benefits. This can be dangerous, and there’s a ceiling to caffeine’s effects, as consuming more doesn’t always produce greater benefits (21).


You can overcome caffeine tolerance by decreasing your daily intake of caffeine, consuming it less often, or consuming more than you normally do. However, the last option is not recommended.

Research suggests that healthy adults can safely consume up to 400 mg of caffeine per day (22).

Pregnant women should consume no more than 200 mg of caffeine per day, with some research suggesting an upper limit of 300 mg per day (23, 24).

For reference, below is a list of popular caffeine-containing beverages and their caffeine content (25, 26, 27, 28):

  • Coffee: 96 mg per 1 cup (8 ounces or 240 mL)
  • Standard energy drink: 72 mg per 1 cup (8 ounces or 240 mL)
  • Green tea: 29 mg per 1 cup (8 ounces of 240 mL)
  • Soft drink: 34 mg per 1 can (12 ounces or 355 mL)

The recommendations for safe caffeine intakes include caffeine from all sources.

Keep in mind that many dietary supplements like pre-workout supplements and fat burners, as well as some over-the-counter pain relievers, such as Excedrin or Midol, contain caffeine.

The caffeine in these products may be synthetically produced or come from natural sources, such as green coffee beans, guarana, or yerba mate.

Containing 16 mg per ounce (28 grams), dark chocolate can also be a significant source of caffeine when consumed in large amounts (29).


Research suggests that healthy adults can safely consume up to 400 mg of caffeine per day. Pregnant women should consume less than 300 mg per day, with some research suggesting no more than 200 mg daily.

Many people consume caffeine-containing beverages like coffee, tea, and soft drinks for their energizing effects.

Regularly drinking these beverages increases adenosine receptors in your brain, allowing more adenosine molecules to bind them. This can increase your body’s tolerance to caffeine’s stimulating effects over time.

You can reduce your tolerance to caffeine by decreasing your daily intake or consuming it less often, such as once or twice per week instead of daily.

Increasing your daily caffeine intake above what you normally consume can also reduce tolerance in the short term, but this is not recommended.