Main Findings
In the current study, we found that several child and maternal sociodemographic factors were related to methylphenidate treatment initiation. In our study, we were able to examine these determinants stratified by the presence and absence of clinically relevant ADHD symptoms. Our findings show that methylphenidate was more frequently prescribed to boys than girls. It also shows that children of mothers with a non-western background were less likely to receive a methylphenidate treatment than children of mothers with a Dutch-Caucasian or other western background. These findings are both in line with results that have been shown in previous studies [
9,
10,
37]. However, the previous studies only addressed the association with sociodemographic factors in patients with an ADHD diagnosis. In our study, we found that even when no ADHD symptoms were reported by mothers, boys and children born to mothers with a western ethnic background were still more likely to receive methylphenidate. Furthermore, we found that a low and secondary maternal education (compared to a high education) was associated with methylphenidate prescription in children without reported symptoms. A previous study of Russel et al., found no significant association between maternal education and medication use in children in a UK population [
8]. This could also be explained by the differences in the educational system of the Netherlands and the UK. It is also possible that they did not find the association as they only explored the sociodemographic factors of medication use among children with ADHD.
Explanations for These Findings
First, sex differences with regard to use of methylphenidate or other stimulants is probably related to the diagnosis of ADHD, which is more common in boys than girls [
38]. This could be explained by the fact that ADHD was once thought to be a predominantly male disorder [
39]. Boys with clinically ADHD, present more outwardly signs of ADHD, such as hyperactive and impulsive behavior, while girls present more inwardly signs, such as inattentiveness and low self-esteem (attention deficit disorder, ADD)[
40‐
42]. This may both lead to boys being diagnosed with ADHD more often as well as earlier initiation of pharmacological treatment as shown previously [
8]. However, in our study we observed that girls are still less likely to receive methylphenidate irrespective of the presence of ADHD symptoms. It is possible that girls may be less qualified as their symptoms are not considered severe enough [
43]. Parents may find it more difficult to cope with the hyperactive and impulsive behavior, which is more prevalent in boys and are therefore more likely to seek help by visiting the GP. This could also be the reason why boys are more likely to be diagnosed and treated with medication. It could imply that girls with ADHD symptoms are undertreated while on the other hand boys without ADHD may be overtreated [
44]. It has also been noted that treatment programs are mainly focused on behavior management, which has a higher priority among boys than girls [
45]. The difference in the symptom profile among boys and girls may be a reason why boys are more frequently prescribed methylphenidate than girls [
46].
Second, we showed that children without ADHD symptoms of mothers who only had limited education (no education, primary and secondary education) were more likely to receive a methylphenidate prescription. On the other hand, no significant association with maternal education was observed in children with ADHD symptoms. This finding might be interpreted that as long as the child has ADHD, there is no problem with inequity. When it comes to children without a diagnosis, there is inequity in treatment. However, these results should be carefully interpreted due to the association of missing information of ADHD symptoms and maternal education. Nevertheless, a previously published study showed that a low maternal education was associated with less involvement in the decision-making of medication initiation in children. Parents may not have sufficient knowledge about ADHD and feel that it is necessary to initiate methylphenidate when this is not thoroughly discussed with them [
47]. Furthermore, we found that children of mothers with a western ethnic background who received a lower education, were more likely to receive methylphenidate than children whose mother received a high education. It may seem that only mothers with a western ethnic background with a low education are less likely to be involved. This association was not found in the non-western group. This may suggest that mothers with a non-western background, irrespective of educational level, are treated differently than mothers with a western ethnic background.
Third, children with ADHD problems and parents from ethnic minority groups may have less access to healthcare or less communication with healthcare professionals due to a language barrier [
23,
24,
48‐
51]. They may also receive less appropriate diagnoses or treatments as the symptoms observed for these disorders may differ across ethnic groups, and may differ from what clinicians are trained to expect [
52,
53]. ADHD problems are also often recognized by teachers when children are more hyperactive than others. However, not all parents may consider hyperactivity as a behavioral problem as some parents may have a positive attitude towards a child with high energy [
54]. This view and recognition of ADHD related problems may vary across different ethnic groups. Furthermore, ethnic minority families may also be less likely to recommend medication and may prefer behavioral therapy over stimulant medication as found in previous studies [
55,
56]. The findings of the current study may reflect cultural differences, knowledge and perceptions about ADHD and its pharmacological treatment. These cultural differences may include behavioral expectations and tolerance, attachment, attention, personality and many other aspects of parenting. It does not only influences the environment in which a child with ADHD functions, but also in the way this child is understood and treated by its parents [
57]. It may also influence the decision to visit a GP or not as some parents may not recognize emotional and behavioral problems as such. A previous study showed that significantly higher scores of hyperactivity were given in China and Indonesia compared to other countries such as the US [
57]. However, it is also possible that parents prefer to seek for other ways to cope with the hyperactivity or emotional problems of their child as they do not want to put their child on chronic medication.
These characteristics may be associated with certain medication types [
58,
59,
60]. However, we have tested this with other medications such as SSRIs, antihistamines and NSAIDs. We found that children born to a mother with a non-western background or a low education were more likely to receive these medications (see supplemental Table
1). As prescribing of methylphenidate was less likely in girls and the non-western group, as can be seen in Table
3, this suggests that symptoms of these children may less readily considered as a problem.
Strengths and Limitations
Strengths of our study are the relatively large population-based cohort, its prospective design, independent registration of dispensed medicines, and the multi-ethnic nature of the sample which limit the chance of selection and information bias. Treatment initiation was based on pharmacy dispensing records, which is more accurate in terms of dispensation date than information on prescription medication from medical records or questionnaires as medication can be prescribed but not collected at pharmacies. However, our study also has some limitations. One of the limitations is that we had to rely on questionnaires filled out by mothers to assess the presence of ADHD symptoms. These mother reports are considered valuable as they provide more insight into the perspective of the mothers with regard to their child’s behavior as ADHD symptoms are not always recognized as such across different demographic groups. However, not all mothers completed the CBCL questionnaire, which is also considered as an important limitation as we were not able to assess the presence of ADHD symptoms in these groups. Information bias may have occurred if the association between maternal characteristics or sociodemographic factors and treatment initiation is different for responders and non-responders, but this is difficult to ascertain. Nevertheless, the stratified analysis in the group without information on ADHD symptoms showed similar results for sex and ethnicity, except for maternal education. Further research is needed to assess the role of maternal education in the treatment initiation of methylphenidate, in particular in relation to the presence of ADHD symptoms. Another limitation is that pharmacy records were not available for half of the participants of The Generation R study as not all pharmacists provided consent to obtain the dispensing records from their pharmacies. As shown in the results, we found that mothers of children without pharmacy records differed on several aspects. Despite this selection bias, we observed similar results in our study compared to the available literature showing an association between initiation of methylphenidate and ethnicity, maternal education level and smoking during pregnancy [
47,
61]. Furthermore, no information about other treatments (e.g. behavioral therapy) was available. Therefore, we were not able to assess if specific demographic groups were receiving behavioral therapy or no therapy at all. Finally, information about maternal characteristics were not available for each child, but the non-response analysis showed no significant differences between both groups.