Cannabis-Induced Psychosis Incidence Rose Across All Three Scandinavian Countries While Alcohol-Induced Psychosis Declined | Research

The takeaway

Using population-wide registry data from Denmark, Norway, and Sweden, cannabis-induced psychosis incidence increased in all three countries (doubling in Denmark from 2.6 to 5.6 per 100,000), while alcohol-induced psychosis declined, with younger patients and higher parental education emerging as trends.

Psychiatrists, public health officials, drug policy researchers, epidemiologists.

Cannabis-induced psychosis incidence doubled in Denmark from 2000 to 2016

What the researchers found

Cannabis-induced psychosis incidence increased in all three countries: Denmark (2.6 to 5.6), Sweden (0.8 to 2.7), Norway (1.8 to 3.0 per 100,000). Alcohol-induced psychosis decreased: Denmark (4.9 to 1.5), Sweden (4.5 to 2.2). Overall substance-induced psychosis rates remained stable (9.3-14.1). Median age at diagnosis decreased. Rates were higher in men and disability pension recipients.

Why it matters

The consistency across three countries with different cannabis policies strengthens the finding that cannabis-induced psychosis is genuinely increasing. The simultaneous decline in alcohol-induced psychosis suggests a shifting substance use landscape with distinct mental health implications.

The numbers in context

Cannabis-induced psychosis: Denmark 2.6 to 5.6, Sweden 0.8 to 2.7, Norway 1.8 to 3.0 per 100,000. Alcohol-induced psychosis: Denmark 4.9 to 1.5, Sweden 4.5 to 2.2. Median age: Denmark 36 to 29, Sweden 41 to 31 years.

How the study worked

Population-wide registry study covering entire adult populations of Denmark and Sweden (2000-2016) and Norway (2010-2015), estimating annual incidence rates per 100,000 by substance type, age, gender, and socioeconomic background.

What this study cannot tell us

Registry data depend on diagnostic practices, which may have changed over time. Increased awareness of cannabis-induced psychosis could inflate apparent incidence. Cannot control for changes in cannabis potency or use patterns. Norway data covers a shorter period (2010-2015).

How to read the evidence

Population-wide registry data covering entire national populations of three countries over 16 years.

When this study was published

Published in 2023 using data from 2000-2016.

The bigger picture

The declining age at diagnosis is particularly concerning, suggesting younger people are experiencing cannabis-induced psychosis. The finding that increases were greatest among those with highly educated parents challenges assumptions about who is most affected.

Questions still open

Is the increase in cannabis-induced psychosis driven by higher cannabis potency, greater use, or better detection?
Why did incidence increase more among those with highly educated parents?

Common questions

Is cannabis-induced psychosis becoming more common?

Yes. Registry data from Denmark, Norway, and Sweden all showed increasing incidence of cannabis-induced psychosis, with rates doubling in Denmark from 2.6 to 5.6 per 100,000 between 2000 and 2016.

Are younger people more affected?

The median age at first cannabis-induced psychosis diagnosis decreased from 36 to 29 in Denmark and from 41 to 31 in Sweden during the study period.

Read the original research

Annual incidence of substance-induced psychoses in Scandinavia from 2000 to 2016.

Psychological medicine, 53(11), 5246-5255

View on PubMed ↗Publisher’s paper ↗

Citation

Rognli, Eline Borger; Taipale, Heidi; Hjorthøj, Carsten; Mittendorfer-Rutz, Ellenor; Bramness, Jørgen G; Heiberg, Ina H; Niemelä, Solja. (2023). Annual incidence of substance-induced psychoses in Scandinavia from 2000 to 2016.. Psychological medicine, 53(11), 5246-5255. https://doi.org/10.1017/S003329172200229X