What did a study of self-selected cannabis show about remembering a story?
A person’s ability to recount a passage after using cannabis can be measured under study conditions. Translating the result to a particular witness takes a separate look at the exposure and the circumstances of the statement.
How the study grouped participants
Morgan and colleagues tested 134 cannabis users twice, roughly a week apart. Each was tested once drug-free and once after smoking their own cannabis. The researchers analyzed samples of the cannabis and saliva and compared the groups at the high and low ends of cannabis CBD content. The low-CBD group showed poorer prose recall while intoxicated, while the high-CBD group did not show the same pattern. Psychotic-like symptom ratings increased in both groups.
Why product choice limits the inference
Participants chose their own cannabis. CBD content was therefore a measured characteristic of a product people selected, rather than an assigned intervention. The comparison cannot isolate CBD from every difference in product choice or smoking behavior. When evaluating an individual statement, separate the time of use, the time the person first learned the information and the time they recalled it. The study measured recall on a specified task and did not test the accuracy of testimony.
Morgan et al., British Journal of Psychiatry
