The most important result of this investigation, based on hair testing for drugs of abuse in children, is the consistent unsuspected high prevalence of pediatric exposure to psychotropic drugs during the last 15 years in Barcelona, Spain. Even though the age of the children was different in the three study cohorts, the percentage of exposed children remained around 25% for ten years, with a raise up to 28% in the more recent past. Apparently, this is due to the appearance of passive exposure to cannabis products in 2013, which was not observed in 1998 nor in 2008.

It has to be said that in 2008, the limit of quantification for the gas chromatographic-mass spectrometric assay available at that time, was of 0.2 ng/mg hair for all the analytes under investigation, including Δ9-tetrahydrocannabinol, the principal hair biomarker of exposure to cannabis products. Most probably, this value was not sensitive enough to disclose eventual exposure to cannabis products and this has been a study limitation at that time. Indeed, the Society of Hair Testing recommended a confirmatory cut-off of 0.05 ng Δ9-tetrahydrocannabinol per mg of hair [9]. However, when hair samples from the 1998 Study 1 cohort were recently examined applying the limit of quantification of 0.05 ng/mg hair, no positive samples were found, showing that at least in 1998 none of the children of study cohort was exposed to cannabis product. This occurrence cannot be attributed to eventual degradation of Δ9-tetrahydrocannabinol in hair samples, which was indeed never observed. Conversely, what it can be said is that in the last 15 years cannabis consumption has increased significantly in Spain with a diffused “social acceptance” of cannabis consumption [2].

Nonetheless, it has to be recognized that the limits of quantification of 0.05 ng/mg could be still high enough to realistically disclose pediatric passive exposure to cannabinoids, particularly for older children who are not in such close contact with the consuming parents. Indeed, this observation suggests that the obtained results could have been conservative and that percentages of pediatric exposure to psychotropic drugs could have been even higher. Overlapping percentages of passive exposure to drugs in children of different age (infants, pre-school and primary school children) evidences that the phenomenon covers all the first childhood (up to 10 years) with no impact of familiar socioeconomic status or nationality, even if the examined children all come from a population of general low socio-economic status for the European standards. What was also already reported for Studies 2 and 3 is that the first source of paediatric exposure to drugs of abuse is the parent, in the majority the cases the mother, and more in general a risky parental environment or contaminated surroundings. Indeed, hair concentrations of cocaine and benzoylecgonine were higher in younger children from Study 2 more exposed than elder ones because of closer contact to the consuming adults, as previously demonstrated [10].

While it has been proved that acute exposure to cocaine during childhood is associated with neurologic manifestations such as focal and generalized seizures in children and toddlers and alterations in mental status, including delirium stupor and coma in older children [11,12], the long term effects of a repeated postnatal exposure to cocaine have not been clarified yet. Similarly, whereas acute exposure to cannabis in childhood was reported to cause developmental delay, hyperactivity, lethargy ataxia, and respiratory insufficiency [13,14], no information on the effects of chronic pediatric exposure to that drug is known. Nevertheless, even if it is difficult to identify a core set of physical, cognitive, or behavioural problems that can be directly attributed to postnatal (or pre- and postnatal) exposure to drugs of abuse, it has been widely demonstrated that paediatric exposure to drugs of abuse is frequently associated with poor child care by the care giver. In this concern, Studies 2 and 3 showed that parents of children exposed to drugs of abuse present, to a significantly higher extent, behavioural patterns with potential harmful effects for the child’s health (e.g., tobacco smoking, cannabis use, benzodiazepines and/or antidepressant use, shorter breastfeeding time) [5,8].

Interestingly, in the same environment, in 2004 we reported on a hidden prenatal chronic exposure to cocaine in 4.4% of newborns, together with 5.3% and 8.7% exposure to cannabis and opiates, respectively [6].

Taken together, all these alarming outcomes demonstrate that, when occurring, passive exposure to drugs of abuse is likely maintained throughout childhood, In contrast to tobacco smoking, at present there is not any restrictive legislation on environmental exposure of children to psychoactive drugs. Indeed, whereas the public health system regularly checks the general population and adolescents for consumption of drugs of abuse using self-reported questionnaires surveys [1,2], no screening inquiries or interventions to reduce prenatal or postnatal exposure have been ever put in place.

The present and previous results on this matter let us hypothesizes that these children receive poor familiar attention, in a country like Spain, where drug exposed children are not protected by any specific law promoting foster care or programmed social intervention. Furthermore, it is clear that consumer parents or care givers responsible for their children’s passive exposure are not aware of this risk and possible deleterious health consequences thereof.