Despite these minor limitations, this study has substantial clinical and methodological importance. First, the ability to measure hourly fluctuations in substance use, psychosis, and negative mood states can help advance our knowledge of the temporal relationships among events, behavior, and internal experience. The results of this study provide support for the growing consensus that cannabis and perhaps other drugs can trigger psychotic symptoms. In turn, the results of this study also provide support for prior claims of self-medication for dysphoria (10), since cannabis and alcohol use followed the experience of psychotic symptoms and negative mood states. In sum, it appears that the "arrow" of cause and effect is circular and points back onto itself. Second, the authors have further validated the use of computerized ambulatory monitoring techniques for collecting real-time data in a challenging clinical population. This technique could potentially be extended to estimate the quantity, frequency, and duration of a variety of behaviors and internal psychological states in many other groups of patients. Moreover, it could be utilized in the context of treatment to better understand adherence to, and the effects of, psychotropic medications on an hourly or daily basis.