Coming across a Psychology Today article on “The Link Between Cannabis and Psychosis” is a little like watching this clip from The Onion. It’s a well written article but someone in a different mental state might read it as “everyone knows you’re high and it’ll probably make you go insane.” I have taken enough econometrics to suspect that there might be some selection effects in the observational studies that this article mentions. I’ve also taken enough econometrics to wonder whether I could answer this question for myself. This post chronicles my attempt to do just that.
Is the problem of finding this evidence that you’ve searched for associations with schizophrenia rather than psychosis more broadly defined? That’s all well and good but if you follow up people who experience cannabis induced psychosis, four years later roughly 1/4 to 1/2 transition to schizophrenia https://academic.oup.com/schizophreniabulletin/article/46/3/505/5588638#
1. Schizophrenia is diagnosed between the ages of 15-35, so the derivative of incidence might just capture the millennial cohort distinct from Gen X and Z. If net MJ consumption goes up but adolescent consumption goes down then macro scale analysis will be too heavily confounded.
2. The medical literature suggests an effect of regular heavy/daily use but not intermittent use; the risk is more like pain pill overdoses than tobacco carcinogens. If everyone smokes 1 extra joint per week because of legalization, that might affect marginal incidence in the 5+ joints-a-week population, but everyone else will be fine.
3. Cannabis can cause psychotic episodes, which shows it impacts the same systems that drive schizophrenia. But, it’s possible that someone who has multiple cannabis-induced psychotic episodes across years satisfies the DSM-V criteria but isn’t a ‘true’ schizophrenic. Does that make our priors go up or down?
I’ve done a bit of research on this topic earlier, which left me mildly concerned about weed and very concerned about the quality of illicit drug studies. Your post is a great attempt but GIGO. Thanks for the attempt tho.
Whoa, very cool. Where did you learn the methodology for synthetic (weighted average) difference-in-difference? I think you described it to me in the past with regards to a different research domain.
Second, can you clarify this: "we can do placebo tests on the control group states that never legalized and see how Colorado’s deviation from its control group compares to these placebos that didn’t actually change their cannabis policies"
Are you comparing [Colorado vs. synthetic Colorado] to [non-legal states vs. their synthetic counterparts]?
Lastly, it's sad that the schizophrenia data is scarce; the "Schizophrenia by State" graph is a very honest inclusion, but I think it reveals that your overall approach doesn't work because the state trends are endogenous.
I think you have overlooked a lot of evidence that cannabis (particularly THC) causes psychosis - summarised in this thread https://twitter.com/psychunseen/status/1504138625713246210?s=46&t=h_aFsZlD-I_rxx3iml2TfA
- and also see this meta https://pubmed.ncbi.nlm.nih.gov/26884547/
Is the problem of finding this evidence that you’ve searched for associations with schizophrenia rather than psychosis more broadly defined? That’s all well and good but if you follow up people who experience cannabis induced psychosis, four years later roughly 1/4 to 1/2 transition to schizophrenia https://academic.oup.com/schizophreniabulletin/article/46/3/505/5588638#
1. Schizophrenia is diagnosed between the ages of 15-35, so the derivative of incidence might just capture the millennial cohort distinct from Gen X and Z. If net MJ consumption goes up but adolescent consumption goes down then macro scale analysis will be too heavily confounded.
2. The medical literature suggests an effect of regular heavy/daily use but not intermittent use; the risk is more like pain pill overdoses than tobacco carcinogens. If everyone smokes 1 extra joint per week because of legalization, that might affect marginal incidence in the 5+ joints-a-week population, but everyone else will be fine.
3. Cannabis can cause psychotic episodes, which shows it impacts the same systems that drive schizophrenia. But, it’s possible that someone who has multiple cannabis-induced psychotic episodes across years satisfies the DSM-V criteria but isn’t a ‘true’ schizophrenic. Does that make our priors go up or down?
I’ve done a bit of research on this topic earlier, which left me mildly concerned about weed and very concerned about the quality of illicit drug studies. Your post is a great attempt but GIGO. Thanks for the attempt tho.
Whoa, very cool. Where did you learn the methodology for synthetic (weighted average) difference-in-difference? I think you described it to me in the past with regards to a different research domain.
Second, can you clarify this: "we can do placebo tests on the control group states that never legalized and see how Colorado’s deviation from its control group compares to these placebos that didn’t actually change their cannabis policies"
Are you comparing [Colorado vs. synthetic Colorado] to [non-legal states vs. their synthetic counterparts]?
Lastly, it's sad that the schizophrenia data is scarce; the "Schizophrenia by State" graph is a very honest inclusion, but I think it reveals that your overall approach doesn't work because the state trends are endogenous.
This is awesome, thanks for doing this and writing it up!