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Caffeine is a stimulatory anti-sleep compound extracted from coffee beans. Habitual caffeine use leads to tolerance, which dulls several of caffeine’s effects.

Our evidence-based analysis on caffeine features 580 unique references to scientific papers.

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Summary of Caffeine

Primary information, health benefits, side effects, usage, and other important details

What does caffeine do?

Caffeine comes from coffee beans, but it can also be synthesized in a laboratory. It has the same structure whether it’s in coffee, energy drinks, tea or pills.

Caffeine is a powerful stimulant, and it can be used to improve physical strength and endurance. It is classified as a nootropic because it sensitizes neurons and provides mental stimulation.

Habitual caffeine use is also associated with a reduced risk of Alzheimer's, cirrhosis, and liver cancer.

Caffeine’s main mechanism concerns antagonizing adenosine receptors. Adenosine causes sedation and relaxation when it acts upon its receptors, located in the brain. Caffeine prevents this action and causes alertness and wakefulness. This inhibition of adenosine can influence the dopamine, serotonin, acetylcholine, and adrenaline systems.

Habitual caffeine use leads to tolerance. This means the effects of caffeine will be diminished, often to the point where the only benefit a user experiences is caffeine’s anti-sleep effect. This is an ‘insurmountable’ tolerance, which means more caffeine will not overcome it. A month-long break from caffeine will reduce tolerance.

For practical tips on the optimal use of caffeine, check out our Supplement Guides.

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How to Take

Recommended dosage, active amounts, other details

Caffeine dosages should be tailored to individuals. If you are new to caffeine supplements, start with a 100mg dose. Typically, 200mg of caffeine is used for fat-burning supplementation, while acute strength increases occur at higher doses, 500mg and above. Researchers tend to use a dosage range of 4-6mg/kg bodyweight.

Caffeine can be supplemented through popular beverages, like coffee, tea and energy drinks, but it can also be taken in a pill form.

Many of caffeine’s effects, including fat burning, strength benefits, and euphoria, are subject to tolerance, and may not occur in people used to caffeine, no matter how large the dose is.

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Human Effect Matrix

Unlocked for Examine members

The Human Effect Matrix summarizes human studies to tell you what effects Caffeine has on your body, how much evidence there is, and how strong these effects are.

Full details are available to Examine members.
Grade Level of Evidence
Robust research conducted with repeated double-blind clinical trials
Multiple studies where at least two are double-blind and placebo controlled
Single double-blind study or multiple cohort studies
Uncontrolled or observational studies only
Level of Evidence
? The amount of high quality evidence. The more evidence, the more we can trust the results.
Outcome Magnitude of effect
? The direction and size of the supplement's impact on each outcome. Some supplements can have an increasing effect, others have a decreasing effect, and others have no effect.
Consistency of research results
? Scientific research does not always agree. HIGH or VERY HIGH means that most of the scientific research agrees.
grade-b Notable Moderate See all 7 studies
Appears to benefit anaerobic cardiovascular exercise, perhaps due to combination antifatigue effects and increasing power output
grade-b Notable Very High See all 9 studies
There appears to be a reliable and significant increase in power output (both weight lifting as well as cycle ergometer measurements) in both trained and sedentary persons with doses of caffeine exceeding 5mg/kg, assuming the subject is not caffeine tolerant. Tolerance, or lower doses of caffeine, are not as effective.
grade-b Minor Very High See all 3 studies
Serum catecholamines (adrenaline, noradrenaline) are increased in naive users of caffeine following acute ingestion
grade-b Minor Very High See all 3 studies
An increase in aerobic exercise capacity is noted with caffeine, possibly secondary to increased free fatty acids and adrenaline
grade-b Minor High See all 3 studies
There may be an acute increase in blood glucose when caffeine is paired with a carbohydrate containing meal, but long term ingestion of caffeine does not appear to adversely influence glucose (only acutely)
grade-b Minor Very High See all 6 studies
Seems to increase lactate production during exercise when caffeine is acutely preloaded
grade-b Minor Very High See all 6 studies
Tends to increase blood pressure more than it doesn't, which is in part due to caffeine tolerance (naive users experiencing increases in blood pressure at higher rates) or genetics; the increase in blood pressure tends to be transient and low in magnitude
grade-b Minor High See all 4 studies
In general, cortisol appears to be increased at high doses of caffeine; lower doses may not have an effect.
grade-b Minor Very High See all 3 studies
An increase in fat oxidation appears to be apparent (assessed via increased serum glycerol and free fatty acids) which is thought to be secondary to increases in adrenaline
grade-b Minor High See all 6 studies
An increase in heart rate is noted, but not wholly consistent. It appears to affect those with lower caffeine tolerance or high overdoses of caffeine
grade-b Minor High See all 4 studies
A decrease in insulin sensitivity is noted acutely when caffeine is taken alongside carbohydrates, thought to be secondary to reducing glucose deposition.
grade-b Minor High See all 5 studies
Although the effects are somewhat unreliable, there appears to be a reduction in the rate of perceived exertion associated with caffeine ingestion
grade-b Minor Moderate See all 5 studies
Although the overall effect is unreliable and context dependent, caffeine appears to improve reaction time (possibly at the cost of accuracy)
grade-b Minor High See all 4 studies
A very small (usually 12%) increase is noted in trained athletes consuming caffeine above 250mg prior to exercise, this may be dependent on exercise as studies without exercise fail to find alterations in testosterone. This increase in unlikely to lead to significant testosterone-like effects
grade-b Minor Very High See all 3 studies
There appears to be an increase in training volume (overall work performed during a workout) associated with caffeine ingestion relative to placebo, extending to both weightlifting and anaerobic cardiovascular exercise
grade-b - Low See all 5 studies
Overall, highly mixed effects effects of caffeine on memory. It appears to increase spatial/perceptual memory and reduce working memory (perhaps secondary to overstimulation)
grade-c Notable Very High See 2 studies
Caffeine is reliable and effective in increasing the state of wakefulness and suppressing sedation
grade-c Minor - See study
It is possible for caffeine to be anxiogenic, but requires genetic susceptability to it
grade-c Minor - See study
An increase in blood flow (Flow mediated vasodilation) has been noted with caffeine.
grade-c Minor Very High See 2 studies
Decrease in fatigue have been noted during exercise and during low strenuous physical exercise
grade-c Minor Moderate See 2 studies
Mixed effects on metabolic rate following acute doses of caffeine
grade-c Minor - See study
Appears to be an increase in oxygen uptake with caffeine consumption, may be related to the increase in metabolic rate
grade-c Minor Very High See 2 studies
May increase subjective well being and mood state, possibly secondary to reducing fatigue or from catecholamines
grade-c Minor - See study
Increases in heat production following caffeine consumption have been noted
grade-c - - See study
In men, there does not appear to be a significant suppressive effect of caffeine on appetite.
grade-c - - See study
No significant influences on HDL cholesterol noted
grade-c - Very High See 2 studies
No significant influences on fasting insulin (not postprandial) are noted with caffeine
grade-c - - See study
No significant influences on LDL cholesterol noted
grade-c - - See study
No significant influence on triglyceride levels
grade-c - - See study
No significant influence on VO2 max ratings
grade-c - - See study
No significant influence on visual acuity has been noted with caffeine on hand-eye or target-based visual tasks

Studies Excluded from Consideration

  • Confounded with other Energy Drink constitiuents[3]

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Frequently Asked Questions and Articles on Caffeine

The downsides of caffeine intake
Caffeine can have a detrimental impact on your blood pressure, eye pressure, and acid reflux.
Ten tips for better sleep
To feel and perform your best, you don’t just need enough sleep, you need enough quality sleep. We break down what you can do — and what you should avoid — to sleep well and wake up refreshed.
How much caffeine is too much?
For healthy adults, up to 400 mg/day is considered safe. Pregnant or breastfeeding women are advised to consume no more than 200 mg/day. People with cardiovascular health issues should also consider limiting their caffeine intake.
How does caffeine work in your brain?
Over the course of a day, you get sleepy as adenosine binds to A1 receptors in your brain. Caffeine blocks adenosine from binding, thus making you feel alert and also helping you feel better.
The science behind caffeine
Why a little bit less caffeine can make it even more powerful...
Are energy drinks bad for you?
Case studies have linked energy drinks to adverse effects, especially on the cardiovascular system, but the overall risk of something bad happening is low and context-dependent.
Do I need to cycle caffeine?
There are benefits associated with chronic caffeine consumption, and there are benefits associated with acute caffeine consumption that fade with tolerance; if you like the latter, cycling is mandatory. If you like the former, cycling is not needed
Does caffeine counteract creatine?
There is very little evidence that caffeine counteracts the benefits of creatine.
Do I need to cycle ephedrine?
Surprisingly, ephedrine does not appear to need cycling for the fat burning aspect of it (it may for neurological stimulation and appetite suppression). If using an ECA stack, however, the caffeine may need to be cycled

Things to Note

Primary Function:

Also Known As

Coffee extract, Tea extract, 1, 3, 7-Trimethylxanthine, Liquid crack

Do Not Confuse With

Caffeic acid

Goes Well With

Caution Notice

Caffeine is highly stimulatory and a systemic vasoconstrictor. Caution should be exerted if one is either not used to caffeine ingestion or currently has high blood pressure.

Caffeine should not be used as a supplement in those with cardiac impairments without prior consultation of one's doctor.

Caffeine can also have an effect on ones quality of sleep; while you may be able to fall asleep, it will be of inferior quality.

  • Caffeine is a potent stimulant and typically used as a standard due to its social renown.

  • Metabolic effects of caffeine may vary depending on whether one is 'naive' to caffeine (infrequent user) or 'accustomed' to caffeine (daily user)

  • Metabolic effects may also vary due to genetics, specifically a polymorphism on the CYP1A1/2 enzyme[1]

  • One review notes that, after looking at the differences in metabolism between humans and rats, that a 10mg/kg bodyweight dose in rats is roughly bioequivalent to 250mg in a 70kg person.[2]

  • Caffeine can be affected by some prescription medications such as Fluvoxamine and aromatase inhibitors like Anastrozole

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Click here to see all 580 references.