Hormonal
Caffeine produces dose-dependent psychomotor effects where low doses (250 mg) enhance performance and subjective pleasantness, while high doses (500 mg) impair performance and increase adverse somatic symptoms.
Stick to a moderate dose of caffeine (around 250 mg, roughly two cups of coffee) for optimal performance and mood benefits. Taking a high dose (500 mg) does not improve performance further and significantly increases the risk of anxiety, restlessness, and physical discomfort. Monitor your plasma concentration if possible, but generally, less is more once you pass the moderate threshold.
Both doses enhanced motor performance compared to placebo; however, the high-dose (500 mg) produced more unfavorable subjective effects (tension, palpitations, restlessness) than the lower dose. ... The maximal performance-enhancing effects were found at low to intermediate plasma concentrations (2.5 µg/mL to 12.5 µg/mL), then diminished at concentrations exceeding that range.
Why this rating
Randomized, double-blind, crossover design with healthy volunteers, though small sample size (n=12).
Source
Dose‐Dependent Pharmacokinetics and Psychomotor Effects of Caffeine in Humans
Gary B. Kaplan et al. · The Journal of Clinical Pharmacology · 1997
DOI 10.1002/j.1552-4604.1997.tb04356.x
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