An Update about Cannabis Research
The newest information about research on cannabis was presented at the annual meeting of the American Psychiatric Association, which I attended this weekend. The high level of interest by the clinicians in attendance was clear from the standing-room-only crowd that remained for the full 3-hour session, with many of us staying over to ask more questions from the panel of experts. Here are some of the highlights about what has changed and what remains the same.
1. Later cognitive deficits from heavy use by teens before age 18
The interpretation of the findings from the most cited prospective study of research on cannabis has become muddied by a subsequent re-analysis. When the results of twins in the cohort were considered, one revision of the conclusions is that some of the decline could have been caused by factors other than cannabis use. No one is saying, however, that heavy use by teens and young adults is a good idea.
2. Drugged driving
Accurate prediction of hazardous driving based on THC levels in automobile drivers is not close to being possible. Attempts to apply the alcohol DWI model have been unsuccessful because:
- THC vanishes from blood within 90 minutes and having blood drawn at the site of the arrest is not currently feasible. Assays of oral fluids are still not sufficiently accurate. Urine levels do not necessarily reflect recent use and cannot be equated with impairment
- Behavioral evaluations of impairment are not specific for the effect of THC.
3. Changing patterns of cannabis use in the community
- Two-thirds of Americans now live in states where medical cannabis is legal. While teenage cannabis use has not increased in those states, for adults both use and the incidence of Cannabis Use Disorder have in fact increased. Colorado is the state that is “leading the pack.” Canada will legalize recreational cannabis for the entire country this summer and many are watching to see what this will bring.
- Frighteningly, enough women are now using cannabis but not alcohol or tobacco during pregnancy, that research into its impact on neonates will be feasible in the future.
4. Relationship of cannabis use to psychosis and schizophrenia
The association has been clear for awhile, but recent evidence from research on cannabis is building for a causal relationship, particularly in people who have a first or second degree relative with schizophrenia. The connection is stronger if the amount of use is higher and the use begins at an earlier age.
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