Cannabis-induced psychosis rates more than doubled in Denmark from 2006 to 2016
The incidence of cannabis-induced psychosis in Denmark rose steadily from 2.8 to 6.1 per 100,000 person-years between 2006 and 2016, paralleling increases in THC potency and cannabis use.
Quick Facts
What This Study Found
Cannabis-induced psychosis incidence more than doubled from 2.8 per 100,000 in 2006 to 6.1 per 100,000 in 2016. A corresponding increase occurred in dual diagnoses of schizophrenia with cannabis use disorder. In contrast, alcohol-induced psychosis decreased over the same period, and other substance-induced psychoses showed no trend.
Key Numbers
Cannabis-induced psychosis: 2.8 per 100,000 (2006) to 6.1 per 100,000 (2016). Alcohol-induced psychosis decreased. Other substance-induced psychoses showed no trend. Dual diagnosis (schizophrenia + CUD) also increased.
How They Did This
National registry study using the Danish Psychiatric Central Research Register. Analyzed absolute incidence and incidence rates per 100,000 person-years for cannabis-induced psychosis, other substance-induced psychoses, and dual diagnosis (schizophrenia + CUD) from 1994 to 2016.
Why This Research Matters
The selective increase in cannabis-induced psychosis (while alcohol-induced psychosis declined and others remained stable) suggests this trend is specific to cannabis rather than reflecting general changes in diagnostic practices or healthcare access.
The Bigger Picture
Denmark has seen both rising cannabis use and increasing THC potency during this period. The parallel rise in both cannabis-induced psychosis and schizophrenia with CUD dual diagnoses suggests a real clinical impact that tracking systems are capturing consistently.
What This Study Doesn't Tell Us
Registry data depends on clinical diagnostic accuracy. Cannot directly link individual THC exposure levels to psychosis. Changes in help-seeking behavior or cannabis availability could partially explain trends.
Questions This Raises
- ?How much of the increase is attributable to higher THC potency vs. more widespread use?
- ?Are countries with different cannabis policies seeing similar trends?
- ?Would availability of lower-potency products slow the increase?
Trust & Context
- Key Stat:
- Cannabis-induced psychosis: 2.8 to 6.1 per 100,000 over 10 years
- Evidence Grade:
- National registry covering entire Danish population with consistent methodology over 22 years. Strong for trend detection.
- Study Age:
- 2021 study analyzing Danish registry data from 1994-2016.
- Original Title:
- Annual incidence of cannabis-induced psychosis, other substance-induced psychoses and dually diagnosed schizophrenia and cannabis use disorder in Denmark from 1994 to 2016.
- Published In:
- Psychological medicine, 51(4), 617-622 (2021)
- Authors:
- Hjorthøj, Carsten(11), Larsen, Maria Oku, Starzer, Marie Stefanie Kejser, Nordentoft, Merete
- Database ID:
- RTHC-03202
Evidence Hierarchy
Follows a group of people over time to track how outcomes develop.
What do these levels mean? →Frequently Asked Questions
Could changes in diagnosis explain the increase?
The authors examined this and concluded diagnostic practice changes do not appear to explain the increase, partly because other substance-induced psychoses did not show similar trends.
Did schizophrenia with cannabis use also increase?
Yes. Dual diagnoses of schizophrenia with cannabis use disorder showed a corresponding increase over the same period, suggesting the cannabis-psychosis relationship extended beyond acute episodes.
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Cite This Study
https://rethinkthc.com/research/RTHC-03202APA
Hjorthøj, Carsten; Larsen, Maria Oku; Starzer, Marie Stefanie Kejser; Nordentoft, Merete. (2021). Annual incidence of cannabis-induced psychosis, other substance-induced psychoses and dually diagnosed schizophrenia and cannabis use disorder in Denmark from 1994 to 2016.. Psychological medicine, 51(4), 617-622. https://doi.org/10.1017/S0033291719003532
MLA
Hjorthøj, Carsten, et al. "Annual incidence of cannabis-induced psychosis, other substance-induced psychoses and dually diagnosed schizophrenia and cannabis use disorder in Denmark from 1994 to 2016.." Psychological medicine, 2021. https://doi.org/10.1017/S0033291719003532
RethinkTHC
RethinkTHC Research Database. "Annual incidence of cannabis-induced psychosis, other substa..." RTHC-03202. Retrieved from https://rethinkthc.com/research/hjorthoj-2021-annual-incidence-of-cannabisinduced
Access the Original Study
Study data sourced from PubMed, a service of the U.S. National Library of Medicine, National Institutes of Health.
This study breakdown was produced by the RethinkTHC research team. We analyze and report published research findings without making health recommendations. All interpretations are based solely on the published abstract and study data.