The objective of this project is to evaluate bupropion's ability to lesson the severity of withdrawal symptoms observed following cessation of chronic, heavy marihuana use. Recently, many studies from several laboratories have documented that a definable and significant withdrawal syndrome occurs upon cessation of chronic, heavy marihuana use. This syndrome includes alterations in mood, sleep disturbances, and cognitive performance. The nature and magnitude of the withdrawal symptoms is believed to be a key component to continued use and in thwarting abstinence efforts. Bupropion has been shown to be effective in treating nicotine addiction where many of the withdrawal symptoms are similar to those observed with marihuana withdrawal. Furthermore, there is a possible pharmacological basis for bupropion's ability to affect marihuana reward pathways and possibly lesson withdrawal effects. The ability of bupropion to lesson or relieve increases in dysphoric mood symptoms (e.g. irritability, anxiety, physical tension, depression) following marihuana cessation has not been studied completely. One well-controlled laboratory study showed that bupropion actually worsen withdrawal symptoms, while pilot data from our laboratory and case history information would indicate a beneficial bupropion effect in treating marihuana use. We propose to study the nature, severity, and time course of the marihuana syndrome with and without bupropion treatment. This will be accomplished through recruiting 24 treatment-seeking, marihuana-dependent users and evaluating them in an outpatient setting. In a 21-day double-blind, placebo-controlled study, an analysis of self-reported subjective measures; sleep quantity, quality and continuity; and repeated measures of selected cognitive abilities will be made. Twelve subjects will receive bupropion; 12 will receive placebo. A week's pretreatment with bupropion will take place before cessation of marihuana intake ('quit day'). Bupropion will be administered as 150 mg/day for 3 days, followed by 300 mg/day (150 mg b.i.d.) for the remainder of the study period. Quit Day will occur on Day 8. Measurements of mood, sleep, and performance will be made over the next 13 days. Thus, this study will employ bupropion in a manner similar to its currently approved use in treating tobacco cessation, and it is expected that bupropion will lessen the severity of withdrawal effects from chronic, heavy marihuana use.