American psychologists have found that students who use cannabis more often are less willing to share it with others and less often smoke in company. The work was published in the journal Experimental and Clinical Psychopharmacology.
Over the past ten years, marijuana use among young people in the US has grown: from 18.3% to 28.7% among people aged 19-30. In parallel, diagnoses of "cannabis use disorder" have become more frequent - a condition in which a person cannot stop using the drug despite problems with health or in communication. This prompted scientists to look for behavioral markers distinguishing harmless use from problematic use.
The study involved 89 students at a small private university in the northwestern US. The average age was about 19, and 74% were white. Almost all (96%) used alcohol. The scientists asked them to imagine 100 people ranked by closeness: from a best friend to a casual acquaintance. For seven of them, they had to indicate what share of hypothetical cannabis the student was willing to give away rather than keep for themselves. The answers were converted to a score from 0 to 1: the higher, the more generous the person.
Then participants filled out a questionnaire about actual use over the past 30 days. The researchers summed the days of use of dried marijuana, concentrates and edible products. The median was 4 days. The students were divided into two groups: 46 people with four or fewer "product days" and 43 with a larger number.
It turned out that frequency of use was moderately associated with lower generosity: the correlation coefficient was -0.30. A correlation is a statistical relationship that by itself does not prove causation. In the "heavy" group, the average generosity score was 0.46 versus 0.57 in the "light" group. The difference is medium in size.
Frequency of use was even more strongly associated with whether a person smokes alone: the correlation was -0.40. Overall, 82% of students said they almost always use cannabis with others. But among those who smoked more often, there were fewer such people: 93% in the "light" group versus 70% in the "heavy" group. In addition, 61% of infrequent users got cannabis from friends, while among frequent users the figure was 35%.
The scientists emphasize: the data are cross-sectional, so it cannot be asserted that frequent marijuana use makes people greedy. It is possible that those who already prefer not to share more often smoke alone as well. The sample is small, it contains almost no people with a diagnosed disorder, and use was assessed by self-report. The authors hope that in the future a simple "generosity" test will help identify a tendency toward problematic use.