National Certified Addiction Counselor, Level I (NCAC I) Practice Exam

Caffeine belongs to the xanthines drug family, which is a subclass of alkaloids. Xanthines are purine derivatives and include other stimulants such as theobromine and theophylline. They have a range of effects on the central nervous system, most commonly recognized as stimulants. Caffeine specifically acts as a central nervous system stimulant, promoting alertness and reducing fatigue by antagonizing adenosine receptors.

While it is true that caffeine is an alkaloid, identifying it specifically as a xanthine provides a more precise classification within the larger category of alkaloids. The other options such as phenothiazines and cannabinoids refer to entirely different classes of compounds, with phenothiazines being primarily associated with antipsychotic medications and cannabinoids related to substances found in cannabis. Thus, xanthines is the most accurate answer when it comes to the classification of caffeine.