Initiation of cannabis use during the 80's in Spain. Social perception and heritability

Introduction: Environmental factors, like social perception or tolerance, may influence the heritability of recreational drug use. Such heritability would increase or decrease depending on the role of environmental factors in... [ view full abstract ]

Introduction: Environmental factors, like social perception or tolerance, may influence the heritability of recreational drug use. Such heritability would increase or decrease depending on the role of environmental factors in inter-individual variability. The analysis of the heritability of initiation and maintenance in the consumption, in key moments related to the social perception of this consumption, can shed light on this question. Our objective is to analyze the relative contribution of genetic and environmental factors at the initiation of cannabis use in a sample of young twins at the time of the massive introduction of cannabis in Spain (1980s).

Method: The sample comprised 1609 subjects (55.0% female), aged between 47 and 73 years (mean = 56.8; SD: 7.1), participating in the Murcia Twin Registry (564 monozygotic and 1045 dizygotic). Information on cannabis initiation and current use was collected through a telephone interview. Heritability estimation was performed using structural equation models.

Results: 14.6% of the sample had ever used cannabis. The model fitting suggests that twin resemblance for initiation in cannabis use is due mainly to genetic factors (AE model), with an estimated heritability of 62.4%, 95% CI [44.2, 76.6]. Discussion: The heritability of initiation in cannabis use was high in restrictive social circumstances but with favorable pressure on the part of the reference group. The effect of shared environmental factors is undetectable under such conditions.