Mental alertness
Supplements studied for mental alertness.
Overview
Black Tea has high-strength evidence from six studies for maintaining alertness and focus during the day, mainly through its caffeine content, which boosts attention especially after poor sleep. Caffeine from coffee or supplements also improves wakefulness across 32 studies.
However, caffeine does not fully restore rested performance and most people still perform below well-rested levels. The heatmap and evidence reviews below provide further detail.
Effect graph
Relevant supplements
Relevant supplements sorted by DEX Score.
Studies
Find individual evidence reviews for supplements sorted by DEX Score.
2 supplements for rated at least stars. All purchase bands. No minimum star filter.
Black TeaView supplement →
Consider purchase·★★★★★
How we scored this▸
- Drinking black tea during the day helps keep people alert and focused.
- This is mainly because of its caffeine content, which boosts attention and mental performance, especially after poor sleep.
Browse 6 studies
RCTBlack tea improves attention and self-reported alertness2010
Two double-blind RCTs found black tea improved switch-task accuracy and self-reported alertness versus placebo; benefits were strongest when theanine and caffeine plasma levels were higher.
- Effect
- Benefit
RCTCognitive and physiological effects of an "energy drink": an evaluation of the whole drink and of glucose, caffeine and herbal flavouring fractions2004n=20
In 20 healthy volunteers, a whole energy drink and its caffeine-plus-glucose components improved secondary memory and attention speed versus placebo, suggesting synergy beyond caffeine alone.
- Effect
- Benefit
- Dose
- 75 mg/day
- Population
- Healthy adults
- Participants
- 20
RCTAn evaluation of a caffeinated taurine drink on mood, memory and information processing in healthy volunteers without caffeine abstinence2001n=42
In 42 adults with minimal caffeine deprivation, an 80-mg caffeinated taurine drink improved attention and verbal reasoning versus sugar-free and sugar-containing placebos.
- Effect
- Benefit
- Population
- Healthy adults
- Participants
- 42
RCTEffect of three caffeine doses on plasma catecholamines and alertness during prolonged wakefulness2000
In 50 sleep-deprived adults, caffeine doses up to 8.6 mg/kg improved alertness (sleep latency, sleepiness, reaction time) and raised adrenaline for 1–4 h versus placebo in a dose-related pattern.
- Effect
- Benefit
- Dose
- 8.6 mg/kg
- Population
- Adults
- Ages
- 18–32
RCTThe effects of a low dose of caffeine on cognitive performance1998
In 8 men, 60 mg caffeine from tea or hot water significantly sped reaction time on CANTAB tests within minutes of consumption, detectable on pattern recognition, delayed match-to-sample, and visual search tasks.
- Effect
- Benefit
- Dose
- 60 mg/day
- Population
- Healthy adults
RCTThe effects of black tea and other beverages on aspects of cognition and psychomotor performance1998n=19
In 19 healthy adults, tea (with ~100 mg caffeine) throughout the day prevented the usual afternoon decline in alertness and largely maintained cognitive performance versus caffeine-matched placebo over ~90 min testing periods.
- Effect
- Benefit
- Dose
- 100 mg/day
- Population
- Healthy adults
- Participants
- 19
CaffeineView supplement →
Consider purchase·★★★★★
How we scored this▸
- Taking caffeine (like from coffee or supplements) helps people feel more awake and alert, especially if they haven’t slept well.
- However, caffeine doesn’t fully make up for lost sleep and most people still won’t think or perform as well as if they were well rested.
Browse 32 studies·1 meta-analysis
RCTDaily Caffeine Intake and the Effect of Caffeine on Pilots' Performance After Extended Wakefulness2023n=30
In 30 aeromedically fit subjects after ~17 h awake, a single 300 mg caffeine dose at midnight significantly preserved psychomotor vigilance and tracking performance overnight versus placebo, regardless of daytime caffeine habits.
- Effect
- Benefit
- Dose
- 300 mg/day
- Participants
- 30
MetaEffects of acute caffeine consumption following sleep loss on cognitive, physical, occupational and driving performance: A systematic review and meta-analysis2019
A meta-analysis of 45 sleep-loss studies found acute caffeine improved attention, executive function, reaction time, information processing, driving control, and occupational performance versus placebo.
- Effect
- Benefit
RCTUsing coffee to compensate for poor sleep: Impact on vigilance and implications for workplace performance2018n=69
In 69 adults after poor sleep, coffee improved and stabilized reaction time on a vigilance task, but increased commission errors in poor sleepers, suggesting faster responding without better inhibitory control.
- Effect
- No Benefit
- Dose
- 100 mg/day
- Population
- Adults
- Participants
- 69
Controlled trialThe combination of short rest and energy drink consumption as fatigue countermeasures during a prolonged drive of professional truck drivers2014
In professional truck drivers during 150-min simulated drives, an energy drink with 160 mg caffeine before driving and a 10-min rest at 100 min improved lane control and reduced fatigue versus placebo.
- Effect
- Benefit
- Dose
- 160 mg/day
RCTCaffeine can decrease subjective energy depending on the vehicle with which it is consumed and when it is measured2013
In 90-min testing sessions, caffeine 80 mg in water increased tiredness and hostility later in the day versus water alone, while caffeine in yoghurt transiently increased subjective energy without consistent mood benefits.
- Effect
- Benefit
- Dose
- 80 mg/day
RCTCombined caffeine and bright light reduces dangerous driving in sleep-deprived healthy volunteers: a pilot cross-over randomised controlled trial2013n=12
In 12 sleep-deprived healthy men (ages 20–50), caffeine 200 mg plus bright light at 1 a.m. significantly reduced lane drifting during simulated nighttime driving at 6 a.m. versus caffeine or light alone.
- Effect
- Benefit
- Dose
- 200 mg
- Population
- Healthy adults
- Participants
- 12
- Ages
- 20–50
RCTFaster but not smarter: effects of caffeine and caffeine withdrawal on alertness and performance2013n=212
In 212 medium-high caffeine consumers, withdrawal caused afternoon sleepiness and poorer reaction time; acute caffeine improved physical reaction times in both groups but did not enhance mental alertness in non-low consumers.
- Effect
- No Benefit
- Dose
- 250 mg/day
- Participants
- 212
RCTSleep restriction and serving accuracy in performance tennis players, and effects of caffeine2013
In performance tennis players after 5 h sleep restriction, caffeine 80 mg did not restore serve accuracy versus placebo; sleep loss impaired serving, and caffeine provided no significant benefit.
- Effect
- No Benefit
- Dose
- 80 mg/day
- Population
- Female athletes
RCTAssessing the effects of caffeine and theanine on the maintenance of vigilance during a sustained attention task2012n=27
In 27 adults over a 2-hour SART vigilance task, caffeine 50 mg plus theanine 100 mg reduced error rates over time versus placebo; caffeine alone lowered tonic alpha power, but neither alone improved all attention measures.
- Effect
- Benefit
- Duration
- 4 days
- Dose
- 50 mg
- Population
- Adults
- Participants
- 27
RCTA cognitive and neurophysiological test of change from an individual's baseline2011n=16
In 16 healthy adults, alcohol, caffeine, diphenhydramine, and sleep deprivation were distinguished using combined cognitive performance and EEG sub-scores, with caffeine affecting alertness-related measures in a double-blind crossover design.
- Effect
- Benefit
- Population
- Healthy adults
- Participants
- 16
RCTEffect of caffeine and taurine on simulated laparoscopy performed following sleep deprivation2011n=18
In 18 surgical novices after sleep deprivation, caffeine 150 mg (± taurine) restored laparoscopic simulator speed and economy to rested levels and improved reaction time, though error counts remained elevated versus rested baseline.
- Effect
- Benefit
- Dose
- 150 mg/day
- Population
- Surgical trainees
- Participants
- 18
RCTExpectation of having consumed caffeine can improve performance and mood2011n=88
In 88 participants, expecting caffeine improved attention and psychomotor speed even with placebo; actual caffeine also improved mood and reward responsivity, without a synergistic expectation-by-drug interaction.
- Effect
- Benefit
- Participants
- 88
RCTAcute caffeine consumption enhances the executive control of visual attention in habitual consumers2010n=36
In 36 high-caffeine consumers, 400 mg caffeine improved executive control of visual attention on the Attention Network Test versus lower doses and placebo, while 100–200 mg doses were less effective in this population.
- Effect
- Benefit
- Dose
- 400 mg
- Participants
- 36
MetaCaffeine for the prevention of injuries and errors in shift workers2010
A Cochrane review of 13 trials found caffeine reduced errors and improved cognitive performance in shift workers and sleep-disordered schedules, though evidence quality was moderate and injury outcomes were not measured.
- Effect
- Benefit
- Population
- Shift workers
Controlled trialEffects of 2 adenosine antagonists, quercetin and caffeine, on vigilance and mood2010n=57
In 57 adults, caffeine 200 mg improved vigilance reaction time and self-rated vigor versus placebo; quercetin 2000 mg did not enhance performance or mood, supporting caffeine but not quercetin as a stimulant at these doses.
- Effect
- Benefit
- Dose
- 200 mg
- Population
- Adults
- Participants
- 57
RCTEffects of caffeine and glucose, alone and combined, on cognitive performance2010n=12
In healthy volunteers, combined caffeine 75 mg and glucose 75 g improved sustained attention and verbal memory consolidation versus either alone; caffeine alone improved reaction time but not all memory measures.
- Effect
- Benefit
- Dose
- 75 mg/day
- Population
- Women
- Participants
- 12
- Ages
- 18–25
RCTGlucose and caffeine effects on sustained attention: an exploratory fMRI study2010
In 40 young adults undergoing fMRI during sustained attention, combined caffeine 75 mg and glucose 75 g increased efficiency of visual attention networks versus placebo, though caffeine alone reduced tonic alpha-band activity.
- Effect
- Benefit
- Dose
- 75 mg/day
- Population
- Young adults
RCTL-theanine and caffeine improve task switching but not intersensory attention or subjective alertness2010n=29
In 29 adults, combined L-theanine 97 mg and caffeine 40 mg improved task-switching accuracy versus placebo; caffeine or theanine alone did not significantly change subjective alertness or intersensory attention.
- Effect
- Benefit
- Dose
- 97 mg
- Population
- Healthy adults
- Participants
- 29
RCTThe combination of L-theanine and caffeine improves cognitive performance and increases subjective alertness2010n=44
In 44 young adults, L-theanine 97 mg plus caffeine 40 mg significantly improved task-switching accuracy and self-reported alertness while reducing tiredness versus placebo over 70–120 minutes.
- Effect
- Benefit
- Dose
- 40 mg/day
- Population
- Young adults
- Participants
- 44
RCTSustaining executive functions during sleep deprivation: A comparison of caffeine, dextroamphetamine, and modafinil2009n=16
After 44 h awake in 16 healthy adults, caffeine 600 mg and modafinil 400 mg improved tower-task and WCST performance versus placebo; dextroamphetamine 20 mg also helped, with modality-specific differences across executive tests.
- Effect
- Benefit
- Dose
- 600 mg
- Population
- Healthy adults
- Participants
- 16
- Ages
- 18–36
RCTComparing the benefits of caffeine, naps and placebo on verbal, motor and perceptual memory2008
In healthy adults, caffeine enhanced physical reaction times in medium-high and non-low consumers but did not improve mental alertness in non-low consumers; withdrawal worsened afternoon sleepiness and reaction time before dosing.
- Effect
- Benefit
- Dose
- 200 mg
- Population
- Healthy adults
Controlled trialEffects of caffeine on alertness as measured by infrared reflectance oculography2008n=12
In 12 low-caffeine users, 200 mg caffeine reduced drowsiness on Johns Drowsiness Scale and improved vigilance reaction times for up to 3–4 hours versus placebo in rested participants.
- Effect
- Benefit
- Dose
- 200 mg/day
- Participants
- 12
RCTEffects of dextroamphetamine, caffeine and modafinil on psychomotor vigilance test performance after 44 h of continuous wakefulness2008n=16
After 44 h awake in 53 adults, caffeine 600 mg, modafinil 400 mg, and dextroamphetamine 20 mg all restored psychomotor vigilance versus placebo; caffeine had the shortest duration and most side effects among stimulants tested.
- Effect
- Benefit
- Dose
- 600 mg
- Population
- Healthy adults
- Participants
- 16
Controlled trialL-theanine and caffeine in combination affect human cognition as evidenced by oscillatory alpha-band activity and attention task performance2008n=27
In 27 adults, combined L-theanine 100 mg and caffeine 50 mg reduced tonic alpha power and improved target detection in a cued attention task versus placebo, suggesting enhanced tonic visual attention deployment.
- Effect
- Benefit
- Dose
- 50 mg/day
- Population
- Adults
- Participants
- 27
RCTThe effects of L-theanine, caffeine and their combination on cognition and mood2008
In a crossover study, caffeine 150 mg improved digit vigilance and RVIP accuracy and reduced mental fatigue; combined with L-theanine 250 mg it further improved reaction time and memory, though L-theanine alone increased headache ratings.
- Effect
- Benefit
- Dose
- 250 mg
RCTInfluence of caffeine ingestion on perceived mood states, concentration, and arousal levels during a 75-min university lecture2007
In 10 university students, caffeine before a 75-min lecture significantly increased self-reported alertness, concentration, energy, and anxiety versus placebo.
- Effect
- Benefit
RCTCognitive and physiological effects of an "energy drink": an evaluation of the whole drink and of glucose, caffeine and herbal flavouring fractions2004n=20
In 20 healthy volunteers, a whole energy drink and its caffeine-plus-glucose components improved secondary memory and attention speed versus placebo, suggesting synergy beyond caffeine alone.
- Effect
- Benefit
- Dose
- 75 mg/day
- Population
- Healthy adults
- Participants
- 20
RCTAn evaluation of a caffeinated taurine drink on mood, memory and information processing in healthy volunteers without caffeine abstinence2001n=42
In 42 adults with minimal caffeine deprivation, an 80-mg caffeinated taurine drink improved attention and verbal reasoning versus sugar-free and sugar-containing placebos.
- Effect
- Benefit
- Dose
- 80 mg/day
- Population
- Healthy adults
- Participants
- 42
RCTEffect of caffeine on simulator flight performance in sleep-deprived military pilot students2000
In sleep-deprived military pilot students during simulated flight after 37 h awake, 200 mg caffeine did not significantly improve flight performance versus placebo, though caffeine subjects rated performance optimistically.
- Effect
- No Benefit
- Dose
- 200 mg/day
RCTEffect of three caffeine doses on plasma catecholamines and alertness during prolonged wakefulness2000
In 50 sleep-deprived adults, caffeine doses up to 8.6 mg/kg improved alertness (sleep latency, sleepiness, reaction time) and raised adrenaline for 1–4 h versus placebo in a dose-related pattern.
- Effect
- Benefit
- Dose
- 8.6 mg/kg
- Population
- Adults
- Ages
- 18–32
RCTThe effects of a low dose of caffeine on cognitive performance1998
In 8 men, 60 mg caffeine from tea or hot water significantly sped reaction time on CANTAB tests within minutes of consumption, detectable on pattern recognition, delayed match-to-sample, and visual search tasks.
- Effect
- Benefit
- Dose
- 60 mg/day
- Population
- Healthy adults
RCTThe effects of black tea and other beverages on aspects of cognition and psychomotor performance1998n=19
In 19 healthy adults, tea (with ~100 mg caffeine) throughout the day prevented the usual afternoon decline in alertness and largely maintained cognitive performance versus caffeine-matched placebo over ~90 min testing periods.
- Effect
- Benefit
- Dose
- 100 mg/day
- Population
- Healthy adults
- Participants
- 19
Evidence visualised
Same ratings as above, aggregated so you can see coverage and imbalance.