Our analyses clearly demonstrate the existence of an intrinsic role of each of the two factors considered: the association of reported use of substances with socioeconomic factors is not explained by the specific distribution of family types within the different levels, and reciprocally, the association with family types is not explained by socioeconomic differences across the different types. Further to that, the association with family types seems stronger than that with socioeconomic level for smoking and cannabis, and at the opposite, the association with socioeconomic level seems stronger than that with family type for binge drinking.
Overall, we confirm that adolescents living in non-intact families are more subject to problematic substance use, compared to adolescents living with both their parents, with little difference between the various non-intact configurations. The observed pattern is very coherent, with strong and consistent associations for tobacco, alcohol and cannabis use.
These results are consistent with a large body of literature that already highlighted that adolescents from non-intact families were more prone to experiment and to regularly use psychoactive substances [3, 25,26,27,28,29,30,31,32,33,34]. Several mechanisms have been suggested to explain the association of family structure and adolescent behaviours . First, due to limited parental resources, a lack of supervision or the presence of more permissive rules, adolescents from non-intact families may have lower perception of risk and therefore be more likely to engage in consumption behaviours perceived as problematic. This is a key aspect in sociology of deviance . Second, higher levels of stress are likely within disrupted families, with substance use being resorted to as a coping mechanism for youth when facing this type of adversity. Lastly, socialization models posit the protective role of the interpersonal parent-child ties, which would be closer and stronger in families with two parents.
Over and above this general pattern, there are differences related to the specific family arrangements. Regarding smoking, a study based on data from eleven European countries reported that adolescents living with both parents smoked less than those living with single mothers, and that the latter smoked less than those living with their single fathers, mother-stepfather, or with neither parent . Our findings somewhat accord with this cross-national study, as we find that adolescents living with their mother have the lowest levels of consumption of all non-intact families, but we find additionally that this relative advantage extends to adolescents in shared custody. Further to that, we show that adolescents in parent-stepparent families more frequently report daily smoking than those in shared custody. Overall, those patterns seem to suggest a relative protection from smoking in mother only and shared custody arrangements.
Regarding cannabis and alcohol, in a large cross-national study of data from 37 countries, youth living with both their parents reported less alcohol and cannabis use than those from other types of families . The observed differences were not very large, and the excess consumption was mostly found in father-stepmother families, single father families and grand-parent only families, leading the author to conclude that the absence of the mother may be the common denominator exposing the adolescents to excess substance consumption. Keeping in mind that many of the confidence intervals overlap, our findings tend to corroborate this conclusion for binge drinking, whereas cannabis consumption appears to be more nuanced. Indeed, we found that adolescents in every single type of non-intact families seemed to be at-risk for binge drinking and, to an even greater extent, for cannabis. For binge drinking, the most protective configuration among non-intact families seemed to be the single mother family. For cannabis, adolescents in father single parent as well as those in mother single parent were more frequently cannabis users than those in shared custody, which could be indicative of the importance of the maintenance of the tie with both parents .
Another important contribution is that, in the face of prior inconsistent evidence, our analyses reveal distinctive socioeconomic gradients for the three substance uses. We find that daily smoking is the only behaviour which displays the classical type of gradient (higher consumption in adolescents from lower SES families), with however a flatter pattern in the full model. A study based on the 2008 ESCAPAD survey found similar results: higher tobacco use among youth of modest background but higher alcohol and cannabis use in youth from the most affluent families . In a multilevel study spanning 35 countries, adolescents from low affluent families had an increased risk of weekly smoking compared to adolescents from high affluent families . The authors suggested the role of psychosocial risks faced by low affluent adolescents, in terms of their relationships with their parents, living conditions and school achievements, with smoking constituting a coping behaviour in inadequate family environments. Another important aspect is that adolescents with low SES parents are more likely to grow up in contexts where smoking is common and particularly to have role models such as parents or siblings who smoke . Under the influence of stress, negative events and the role modelling to which they are exposed, they may experiment smoking, and, once they do, the addictiveness of nicotine may lead them to shift from occasional to regular use through adolescence and into adulthood .
The same rationale cannot however be applied to the other two substances. In a literature review on socioeconomic status and health behaviours in adolescence, low SES was associated with greater cigarette smoking, but had no clear pattern of association with alcohol consumption or cannabis use . In the United States, young adults with the highest family background SES were found to be more prone to alcohol and cannabis use . In a database covering 24 European countries, adolescents in lower socioeconomic positions were found to be more likely to report regular smoking and heavy episodic drinking, but there was no association with recent cannabis use . In France, experimenting with tobacco or cannabis occurred more frequently among youngsters from affluent than from modest or underprivileged families, whereas at the opposite, the latter were more prone to engage in daily or regular use after experimenting , and the same applied to binge drinking . We find binge drinking to be more common in the upper SES families, a pattern which may be related to the hypothesis that high SES adolescents engage in negative health behaviours due to the combination of high achievement pressures, increased access to spending money, less adult supervision and permissive parental attitudes , or to the isolation from parents very involved in their demanding careers . Lastly, no visible socioeconomic gradient emerges in our study for cannabis use, and for some authors this lack of association may be interpreted as a reflection of the influence of peers and school environments, outweighing the impact of family SES .
The ESCAPAD survey, given its magnitude and large sample, supplied powerful measures potentially exploitable at different types and sub-types of families. Yet, some limitations are to be noted. First, a confusion between parents and stepparents appeared when interpreting specific parental situations, likely because no distinction was made in the questionnaire. We suggest this nuance should be added in the next editions of the ESCAPAD project. Second, significant non-response rates were observed for socioeconomic variables (probably due to the adolescents’ lack of knowledge or the difficulty to classify the parental occupation) which consequently inflated the lowest socioeconomic categories. However, no distinctive or highly significant association was observed for this category.
Our joint analysis of family structure and socioeconomic profile provides original findings on the intrinsic roles of those two major determinants of adolescent substance use. Family structure is at the forefront, as living in a non-intact family is associated with much higher levels of consumption for all three substances. Socioeconomic factors are less influential, and we find distinctive patterns for the different substances. The strength and the consistency of the association of family structure with the different substances is noteworthy, in a context where non-intact families have become almost the norm  and where the level of drug use is high [18, 19].
It is therefore important from a public policy perspective, to both conduct prevention at the population level, and build more targeted strategies, as the two approaches are complementary. As adolescents from low SES families are more likely to smoke regularly, they could benefit from targeted interventions through school-based or other institution-based prevention programmes, as suggested by Henkel & Zemlin . Tobacco-prevention skill-building programs could be led by teachers, adult facilitators or health professionals, and combine social competence training with training in skills to manage peer pressure . Programs to prevent heavy episodic drinking and cannabis use may be useful in high SES social backgrounds, particularly to develop awareness of the actual adolescent behaviours and encourage the parents to enforce clear rules surrounding substance use . As for the risks faced by adolescents after family disruption, prior research has pinpointed the importance of the qualitative aspects of family life, advising that “programs concerned with youth substance use take a holistic approach that includes families, and peers, and mental health problems” .