Caffeine Optimization Versus Standard Caffeine Dosage (2B-2)

Inclusion Criteria: * Age 18-39 years of age * Must demonstrate adequate comprehension of the protocol by achieving a score of at least 80% correct on a short multiple-choice quiz Exclusion Criteria: * Self-reported habitual nightly sleep amounts outside the target range of approximately 6-9 hours (i.e., less than 6 hours per night or more than 9 hours per night, on average) * Self-reported nighttime bedtimes earlier than approximately 2100 hours on average during weeknights (Sunday through Thursday) * Self-reported morning wake-up times later than approximately 0900 on average during weekdays (Monday through Friday) * Self-reported habitual napping (\> 3 times per week) * Self-reported symptoms suggestive of a sleep disorder (to include but not limited to sleep disordered breathing/sleep apnea, narcolepsy, idiopathic hypersomnia, restless leg syndrome, parasomnias, rapid eye movement (REM) behavior disorder, etc.) * History of a sleep disorder (to include all of the above) * Any use of prescription or over-the-counter sleep aids during the 6-month period prior to screening indicative of a potential sleep disorder as determined by the examining study physician * History of neurologic disorder (e.g., seizure disorder, amnesia for any reason, hydrocephalus, multiple sclerosis) * Self-reported caffeine use \> 400 mg per day on average * Score of 14 or above on the Beck Depression Inventory (BDI) * Score of 41 or above on the Spielberger Trait Anxiety Inventory (STAI-T) * Score below 31 or above 69 on the Morningness-Eveningness Questionnaire * Self-reported regular nicotine use (\> 1 cigarette or equivalent per week) within the last 1 year) or positive nicotine/cotinine result during screening visit * Self-reported heavy alcohol use (≥14 drinks per week or as determined by the examining study physician) or positive saliva alcohol result during screening visit * History of cardiovascular disease (to include but not limited to arrhythmias, valvular heart disease, congestive heart failure, history of sudden cardiac death or myocardial infarction) * Underlying acute or chronic pulmonary disease requiring daily inhaler use * Kidney disease or kidney abnormalities * Liver disease or liver abnormalities * Self-reported history of psychiatric disorder requiring hospitalization or use of psychiatric medication for any length of time * Self-reported use of products or drugs that cannot be safely discontinued during in-laboratory phases (determined on a case-by-case basis by the examining study physician) * Self-reported current use of other illicit drugs (to include but not limited to benzodiazepines, amphetamines, cocaine, marijuana) or positive urine drug screen * (Females only) positive urine pregnancy result * (Females only) self-reported or suspected current breast-feeding or collecting breast milk * Resting blood pressure above 140/90 or resting pulse \> 110 beats per minute (if a physician performs a repeat measurement, \~20 minutes after original measure, and it is within range, volunteer will not be excluded) * BMI ≥ 30 (Obese Class I or greater) * Clinically significant values (as determined by the reviewing study physician) for any hematology or chemistry parameter * Inability to read and sign consent * (Military only) failure to obtain required approved official leave to participate * Failure to cooperate with requirements of the study, e.g. failure to complete 80% of Smart-Psychomotor Vigilance Tests (PVTs) during Phase 1 (Days 2-13)