... The behavioral and biological concomitant of chronic marijuana use were studied in a group of heavy and casual users under controlled research ward conditions. Assessments of operant work performance revealed that most subjects showed no impairment in motivation to work for money reinforcement even when they smoked a large number of marijuana cigarettes. Some dose related decrement in performance was noted following days of heavy marijuana smoking. However, these decrements were probably not biologically significant. No changes were observed in a large series of physical and laboratory assessments following marijuana smoking.
The only significant changes were those related to vital capacity (lung function) and these changes may be more closely related to the processes of smoking per se than to the pharmacological actions of marijuana.
No changes in testosterone level were observed following chronic marijuana smoking. Significant weight gain was associated with marijuana smoking. Marijuana also appeared to influence a number of complex social and psychological factors associated with personal interaction. No evidence was obtained that marijuana produces any significant adverse effects on cognitive or neurological function.