Methylxanthines and drug dependence: a focus on interactions with substances of abuse. 
This chapter examines the psychostimulant actions of methylxanthines, with a focus on the consequences of their excessive use.  Consumption of methylxanthines is pervasive and their use is often associated with that of substances known to produce dependence and to have abuse potential.  Therefore, the consequences of this combined use are taken into consideration in order to evaluate whether, and to what extent, methylxanthines could influence dependence on or abuse of other centrally active substances, leading to either amplification or attenuation of their effects.  Since the methylxanthine that mostly influences mental processes and readily induces psychostimulation is caffeine, this review mainly focuses on caffeine as a prototype of methylxanthine-produced dependence, examining, at the same time, the risks related to caffeine use.