caffeine

This term refers specifically to the chemical stimulant, carrying a clinical and biological connotation. It is typically used in contexts involving nutrition, pharmacology, or daily habits, often associated with alertness, energy, or jitteriness. As a mass noun representing a chemical substance, it is uncountable. To refer to specific quantities or types of the stimulant, speakers must use partitive constructions such as a dose of caffeine or a high level of caffeine.