The purpose of this study is to learn more about the interaction between delta 9 tetrahydrocannabinol (THC) and tolcapone and their effects on behavior and cognition. Tetrahydrocannabinol is the active ingredient of marijuana, cannabis, “ganja”, or “pot”. Tolcapone is a commercially available medication used in the treatment of Parkinson’s disease.  We will measure the effects of THC and tolcapone by using questionnaires and cognitive tasks and collecting blood to measure the THC level and Catechol-O-methyl transferase (COMT) enzyme that metabolizes dopamine, a chemical found in brain. The test sessions will take place at North Shore University Hospital. This study will include 54 male or female cannabis users ranging in age from 18 to 40 years old.