Genetics impact caffeine metabolism. Some genetic polymorphisms make individuals more or less susceptible to caffeine.
Regular caffeine use may cause tolerance, which reduces its stimulating effects. Caffeine dosages may increase over time to maintain alertness and energy.
Caffeine sensitivity varies. Some people are more sensitive to its effects and feel more awake, while others feel less stimulated.
Hormonal factors may modify caffeine's effects. Caffeine may affect women differently during pregnancy or menstruation.
Caffeine is less effective with poor sleep quality. Caffeine may not totally alleviate sleep deprivation.
Metabolism affects caffeine processing. Liver function, enzyme activity, and metabolism affect caffeine metabolism and duration.
Expectations and placebo effects may affect caffeine perception. Beliefs regarding caffeine's efficacy may affect how it feels.