Caffeine

Best for

Strengthen your memory

Likely strong benefit · 80–450 mg/day for 1 weeks · 1 meta-analysis , n=190

94 papers · 18 claims · 123 outcomes scored · 10 positive

Outcomes

What caffeine actually does, by outcome

Each row is one outcome with effect size, evidence base, the dose that worked in trials, and time to first effect. Magnitude tiers come from native-unit MCID where available, Cohen's d otherwise.

Outcome Effect size Evidence Dose Weeks Rank

Sharpen accuracy and agility in sport Likely strong benefit

Execute skills more precisely when fatigue and pressure mount.

13 meta-analyses n=3.5k 1–10 mg/kg 0 wk #1/14

21324203·35010566·37815006·36297081 +9 more

large

13 meta-analyses n=3.5k Meta-analyzed I²=84%

1–10 mg/kg

0 wk

#1 /14

Strengthen your memory Likely strong benefit

Names, conversations, faces, and details stick instead of dissolving.

6 meta-analyses n=190 80–450 mg 1 wk #4/42

33201262·20464765·19777214·25389379 +2 more

large

6 meta-analyses n=190 Meta-analyzed

80–450 mg

1 wk

#4 /42

Sharpen focus and mental stamina Promising early signal

Concentrate longer, resist distraction, and stay mentally sharp through demanding tasks.

15 meta-analyses n=451 1.2–800 mg 0–1 wk #2/40

20464765·25527035·33364521·40704635 +11 more

moderate

15 meta-analyses n=451 Meta-analyzed

1.2–800 mg

0–1 wk

#2 /40

Cut caffeine dependence Promising early signal

Makes caffeine feel less essential and tapering less punishing.

4 RCTs n=197 100 mg 1–27 wk

26501499·30580203·41156489·2794839

moderate

4 RCTs n=197

100 mg

1–27 wk

—

Wake up clear-headed Studies contradict

Less grogginess, more energy from the moment you open your eyes.

7 RCTs n=149 6–800 mg/kg 0–3 wk #6/14

31480553·34024173·19241060·25527035 +3 more

moderate

7 RCTs n=149

6–800 mg/kg

0–3 wk

#6 /14

Last longer before giving out Proven modest benefit

More reps, more miles, and a higher ceiling before fatigue forces you to stop.

25 meta-analyses n=3.9k 1.3–474.78 mg 1 wk #1/40

21526071·25389379·36615805·38568259 +21 more

small

25 meta-analyses n=3.9k Meta-analyzed

1.3–474.78 mg

1 wk

#1 /40

Reduce everyday fatigue Faint early signal

Less of that heavy, worn-out feeling that makes simple tasks feel like a chore.

4 RCTs n=102 3–400 mg 3 wk

19241060·35684105·40369047·2794839

small

4 RCTs n=102

3–400 mg

3 wk

—

Sharpen reasoning and problem solving Faint early signal

See patterns faster and solve logic problems with less effort.

3 meta-analyses n=55 200–800 mg 0 wk #2/6

20464765·33201262·33364521

small

3 meta-analyses n=55 Meta-analyzed

200–800 mg

0 wk

#2 /6

Speed up mental arithmetic Faint early signal

Calculate faster and hold accuracy when numbers pile up.

1 RCT n=32 200 mg — #1/4

33201262

small

1 RCT n=32

200 mg

—

#1 /4

Speed up thinking and reactions Barely detectable

Shortens the gap between seeing a question and having the answer.

10 meta-analyses n=355 1.2–800 mg 0–1 wk

19777214·20464765·33201262·33800853 +6 more

trivial

10 meta-analyses n=355 Meta-analyzed

1.2–800 mg

0–1 wk

—

Blunt blood pressure spikes Proven modest benefit

Keeps your numbers steadier when stress, caffeine, or exertion hits.

10 meta-analyses n=1.5k 50–600 mg 1–5 wk

12392588·25716925·39377163·39747536

small

10 meta-analyses n=1.5k Meta-analyzed

50–600 mg

1–5 wk

—

Fall asleep faster Faint negative signal

Shrinks the gap between hitting the pillow and actually sleeping.

5 meta-analyses n=386 6–450 mg 1–5 wk

31480553·33013662·33633278·36870101 +1 more

small

5 meta-analyses n=386 Meta-analyzed

6–450 mg

1–5 wk

—

Smooth out coffee jitters Not enough research

Buffers the anxious, shaky edge some people get from coffee.

1 meta-analysis n=— 12.5–720 mg —

41549915

—

1 meta-analysis n=— Meta-analyzed

12.5–720 mg

—

Ease caffeine withdrawal symptoms Not enough research

Smooths out the headache, fog, and slump when cutting back on caffeine.

1 RCT n=— 450 mg 1 wk

33633278

—

1 RCT n=—

450 mg

1 wk

—

Lower day-to-day anxiety Likely somewhat harmful

The background hum of worry that colors everything gets quieter.

3 meta-analyses n=650 3–300 mg/kg —

40977612

moderate

3 meta-analyses n=650 Meta-analyzed I²=95%

3–300 mg/kg

—

Ease anxiety in older adults Likely somewhat harmful

Quiets the health worries and body tension that build with age.

2 meta-analyses n=626 300 mg —

moderate

2 meta-analyses n=626 Meta-analyzed I²=95%

300 mg

—

Reduce pre-competition anxiety Likely somewhat harmful

Quiets the overthinking that hijacks execution right before you compete.

2 meta-analyses n=626 300 mg —

moderate

2 meta-analyses n=626 Meta-analyzed I²=95%

300 mg

—

Lower your blood pressure May have slight negative effect

Brings down both systolic and diastolic, especially when baseline runs high.

8 meta-analyses n=949 0–600 mg 1–5 wk

15882556·1747643·25716925·34577880 +4 more

small

8 meta-analyses n=949 Meta-analyzed I²=100%

0–600 mg

1–5 wk

—

Outcome	Effect	Evidence	Dose	Weeks	Rank
Sharpen accuracy and agility in sport Likely strong benefit	large	13 meta-analyses n=3.5k Meta-analyzed	1–10 mg/kg	0 wk	#1/14
Strengthen your memory Likely strong benefit	large	6 meta-analyses n=190 Meta-analyzed	80–450 mg	1 wk	#4/42
Sharpen focus and mental stamina Promising early signal	moderate	15 meta-analyses n=451 Meta-analyzed	1.2–800 mg	0–1 wk	#2/40
Cut caffeine dependence Promising early signal	moderate	4 RCTs n=197	100 mg	1–27 wk	—
Wake up clear-headed Studies contradict	moderate	7 RCTs n=149	6–800 mg/kg	0–3 wk	#6/14
Last longer before giving out Proven modest benefit	small	25 meta-analyses n=3.9k Meta-analyzed	1.3–474.78 mg	1 wk	#1/40
Reduce everyday fatigue Faint early signal	small	4 RCTs n=102	3–400 mg	3 wk	—
Sharpen reasoning and problem solving Faint early signal	small	3 meta-analyses n=55 Meta-analyzed	200–800 mg	0 wk	#2/6
Speed up mental arithmetic Faint early signal	small	1 RCT n=32	200 mg	—	#1/4
Speed up thinking and reactions Barely detectable	trivial	10 meta-analyses n=355 Meta-analyzed	1.2–800 mg	0–1 wk	—
Blunt blood pressure spikes Proven modest benefit	small	10 meta-analyses n=1.5k Meta-analyzed	50–600 mg	1–5 wk	—
Fall asleep faster Faint negative signal	small	5 meta-analyses n=386 Meta-analyzed	6–450 mg	1–5 wk	—
Smooth out coffee jitters Not enough research		1 meta-analysis n=— Meta-analyzed	12.5–720 mg	—	—
Ease caffeine withdrawal symptoms Not enough research		1 RCT n=—	450 mg	1 wk	—
Lower day-to-day anxiety Likely somewhat harmful	moderate	3 meta-analyses n=650 Meta-analyzed	3–300 mg/kg	—	—
Ease anxiety in older adults Likely somewhat harmful	moderate	2 meta-analyses n=626 Meta-analyzed	300 mg	—	—
Reduce pre-competition anxiety Likely somewhat harmful	moderate	2 meta-analyses n=626 Meta-analyzed	300 mg	—	—
Lower your blood pressure May have slight negative effect	small	8 meta-analyses n=949 Meta-analyzed	0–600 mg	1–5 wk	—

Buy well

Recommended Caffeine products

Real products that dose Caffeine where the research does, in a clean formulation, from brands we've audited. We only list ones we'd stand behind.

Chosen for adequate Caffeine dosing vs. the studied range, a clean formulation (grade A–C), and independent brand-quality audits. Not sponsored.

Risk profile

Adverse events and known drug interactions

Safety events

myocardial_infarction severe

stroke severe

arrhythmia severe

seizure severe

psychosis severe

rhabdomyolysis severe

hepatotoxicity severe

exertional_heat_illness severe

Drug interactions

Antihypertensives major decreases effect

Antidepressants major increases toxicity

other major increases concentration

Carbamazepine major decreases effect

Phenobarbital major decreases effect

Phenytoin major decreases effect

Gabapentin major decreases effect

Levetiracetam major decreases effect

Pregabalin major decreases effect

Topiramate major decreases effect

Co-studied with

Supplements that share evidence with caffeine

Theanine 20 shared outcomes · d=0.60
Taurine 13 shared outcomes · d=0.99
Glucuronolactone 13 shared outcomes · d=0.99
Glucose 13 shared outcomes · d=0.99
Tyrosine 11 shared outcomes · d=0.50

Sources

Generated August 14, 2026

Caffeine

What caffeine actually does, by outcome

Recommended Caffeine products

Adverse events and known drug interactions

Supplements that share evidence with caffeine

More evidence for Caffeine

Wide Awake, Wise to the Buzz: How a 500-Year Habit Became a Precision Tool

Best Supplements to Stay Asleep Through the Night

Focus & memory: evidence map across 45 supplements

Sleep: evidence map across 37 supplements

Stress: evidence map across 46 supplements

Citicoline

Caffeine

Recommended Caffeine products

More evidence for Caffeine

NewWide Awake, Wise to the Buzz: How a 500-Year Habit Became a Precision Tool

NewBest Supplements to Stay Asleep Through the Night

NewFocus & memory: evidence map across 45 supplements

NewSleep: evidence map across 37 supplements

NewStress: evidence map across 46 supplements

NewCiticoline

Wide Awake, Wise to the Buzz: How a 500-Year Habit Became a Precision Tool

Best Supplements to Stay Asleep Through the Night

Focus & memory: evidence map across 45 supplements

Sleep: evidence map across 37 supplements

Stress: evidence map across 46 supplements

Citicoline