low to intermediate doses of caffeine , theophylline , 8-phenyltheophylline ( 8-pt ) , 8-cyclopentyltheophylline ( cpt ) , and 3-isobutyl-1-methylxanthine ( ibmx ) produced dose-related increases in response rate , whereas higher doses increased response rate less or decreased it .
C0039771
theophylline
C0000096
3-isobutyl-1-methylxanthine