1. A comparison between North and South of Europe
Does age of first cannabis use and frequency of use influence age of First-Episode Psychosis (FEP)?
A comparison between North and South of Europe
C. La Cascia1, F. Seminerio1, L. Sideli1, L. Ferraro1, A. Mulè 1,2 C. Sartorio1, G. Tripoli1,2, M. Di Forti2,
D. La Barbera1, R.M. Murray2
Affiliations: 1University of Palermo, 2Institute of Psychiatry, King’s College London
Background
Cannabis is one of the most commonly used drugs among young people across Europe (EMCDDA data 2014). Moreover, it is one of the most abused illicit drugs among patients suffering from schizophrenia (Linszen et al., 1994) and, particularly, in patients at their first episode of psychosis (Donoghue et al., 2011).
Furthermore, patients suffering from psychosis with a history of cannabis use have an earlier age of onset of psychosis (AOP) than those who never used it (Di Forti et al., 2014).
We aim to investigate if the reported association between use of cannabis and AOP is consistent across to European samples with expected differences in pattern of cannabis use (i.e. age at first use, frequency of use).
Methods
The data we analyzed are from the European Gene-Environment-Interaction (EUGEI) study. We collected information on 935 first episode psychosis patients (FEP) across Europe and we focused on two areas of Europe: North Europe (NE: UK & Netherland; N=321) and South Europe (SE Spain & Italy; N=356).
We collected socio-demographic data and a detailed history of cannabis use administering the Cannabis Experience Questionnaire (EUGEI study version). For cannabis consumers, frequency of cannabis use was categorized as follows: “only once or twice”(1), “a few times each year”(2), a few times each month (3), (more than) once a week (4) and “every day”(5).
We used a linear regression model, AOP was used as the outcome variable and age of first use and frequency of cannabis use were entered as independent variables.
Table 1. Summary of T test N
Mean Age (SE)
t Student
p value
FEP users
607
29.02 (±9.62)
t=-9.32
p<0.001
FEP never users
328
34.94 (12.5)
FEP under 16 years old
349
25.47 (± 7.03)
t=-9.42
FEP over 16 years old
249
32.05 (±10.05)
NE FEP users
253
28.12 (±8.42)
t=-4.65
NE FEP never users 67
34.18 (±12.68)
SE FEP users
217
t=-5.75
SE FEP never users
139
35.55 (±11.61)
Results
In the total sample, N=935, comparing FEP who were cannabis users with no users, we found a significant difference in mean AOP.
Moreover, cannabis users started at age ≤ 16 years old have earlier age of psychosis onset compared with those who started later.
When the sample was split in NE and SE groups, the mean AOP in cannabis users was lower than non-users both in NE sample and in SE sample (Table 1).
In SE, the percentage of variance explained in a regression model is 31% (R2adj=.30) vs 16% (R2adj=.15) of NE. All predictors are statistically significant. (Table 2)
Table 2. Summary of general linear regression analysis, with split sample (North Europe =UK & Netherland (n=321); South Europe= Spain & Italy; N= (n=356) β
S.E. β t
NE Intercept
22.15
2.53
NE sample age first use
.31
.11
t=5.16*
NE frequency
1.80
.34
t=-2.93*
SE Intercept
21.09
2.758
SE sample age first use
0.41
.119
t=6.67*
SE frequency
-2.87
.367
t=-4.66*
* p<0.01
Discussion
Our results support the association between cannabis use and younger AOP in NE and SE samples, but we did not observe significant difference across Europe. Linear regression model on predictors (age of first use, frequency of use) analyzed in both clinical samples confirmed relationship of causality with dependent variable (AOP), with a higher percentage of explained variance in sample of SE than NE.
So we conclude the association between earlier use of cannabis and earlier AOP is higher in SE than in NE.
Further analyses are needed in order to explain this difference.
References
EMCDDA, Prevalence of Daily Cannabis Use in the European Union and Norway. Publication Office of the European Union, Luxembourg.
Di Forti M. et al.  (2014). Daily Use, Especially of High-Potency Cannabis, Drives the Earlier Onset of Psychosis in Cannabis Users Schizophr Bull 40 (6):
Donoghue et al. (2011) The association between substance misuse and first-episode psychosis in a defined UK geographical area during the 1990s. Social Psychiatry and Psychiatric Epidemiology, Volume 46, Issue 2, pp
Aknowledgments
Special aknowledgments to the EU-GEI team, to the consultants and the doctors of the mental health services of ASP 6, to the Palermo Psychiatric Units of Villa Sofia Hospital,  Cervello Hospital, Ingrassia Hospital, Civico Hospital, Policlinico Hospital and Villa Margherita, Villa Serena and Clinica D'anna private hospitals who have kindly cooperated to the study. Special thanks to the patients and their families for having joined the study.