Caffeine

Won't reliably prevent mental fatigue from sustained cognitive tasks — one study found caffeine performed no better than placebo on mental fatigue measures after a 30-minute Stroop task. Doesn't improve soccer passing skill performance. Beverage temperature (cold vs. tepid) doesn't meaningfully change how caffeine affects your brain during prolonged standing. Not a substitute for actual sleep — it disrupts deep sleep architecture even when you don't notice it.

• Disrupts sleep EEG architecture — suppresses slow-wave (deep) sleep and homeostatic sleep recovery even at moderate doses, especially when taken in the evening
• Regular use can lead to dependence and withdrawal symptoms; study participants were required to abstain 48 hours before pharmacokinetic testing
• High dietary caffeine exposure (from coffee, tea, and supplements combined) can exceed safety thresholds — EU food safety monitoring flagged this concern particularly for adults and the elderly
• Individuals with autonomic disorders, orthostatic intolerance, or syncope risk should use caution — caffeinated beverages did not protect against orthostatic stress in a standing study
• Significant individual variation in metabolism due to CYP1A2 genetic differences means the same dose can affect people very differently