8-Cyclopentyl-1,3-dimethylxanthine (8-Cyclopentyltheophylline, 8-CPT, CPX) is a drug which acts as a potent and selective antagonist for the adenosine receptors, with some selectivity for the A<sub>1</sub> receptor subtype, as well as a non-selective phosphodiesterase inhibitor. It has stimulant effects in animals with slightly higher potency than caffeine.