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Tracking of Medicine Use and Self-Medication From Infancy to Adolescence: 1993 Pelotas (Brazil) Birth Cohort Study

      Abstract

      Purpose

      To track the use of medicine and self-medication from infancy to adolescence.

      Methods

      All newborns in the city of Pelotas, Brazil, were monitored and enrolled in the 1993 Pelotas (Brazil) Birth Cohort Study. Subsamples of the cohort were visited at 1, 3, and 6 months and at 1 and 4 years of age. At 11 and 15 years of age, all cohort members were sought. In each of these visits, information on medicine use in the 15 days before the interview was collected. Two outcomes were analyzed: prevalence of medicine use and prevalence of self-medication.

      Results

      Prevalence of medicine use in the first year of life ranged from 52.0% to 68.6%. From 4 to 15 years of age, the prevalence decreased, ranging from 30.9% to 37.2%. At age 15, girls presented a 33% higher prevalence of medicine use than boys. The proportion of self-medication ranged from 12.4% to 29.0% and was higher in girls aged 11 and 15 years than boys of the same age. In all follow-up periods, use of medicines was significantly higher among children who used medicines in the earlier period. Prevalence of self-medication was higher among those who were self-medicated in the previous periods.

      Conclusions

      Tracking studies are important to public health because they can predict future behavior by analyzing past behavior, thus helping in designing preventive actions. In this study, previous use of medicines predicts future use, thus creating an opportunity to plan actions that promote the rational use of medicines.

      Keywords

      In all waves of data collection of this Brazilian study, which followed up >4,000 individuals from birth to adolescence, use of medicines and self-medication tracked strongly from one period to the next one, thus suggesting that preventive strategies should start as early as possible.
      Rational use of medicines is of concern, independent of age, and becomes even more important in younger ages because there are significant biological differences between children and adults regarding pharmacokinetics and pharmacodynamics of medicines [
      • McCarver D.G.
      Applicability of the principles of developmental pharmacology to the study of environmental toxicants.
      ].
      The international literature shows that medicine use is highly prevalent among children [
      • Sturkenboom M.C.
      • Verhamme K.M.
      • Nicolosi A.
      • et al.
      Drug use in children: Cohort study in three European countries.
      ], especially in the first months of life [
      • Headley J.
      • Northstone K.
      Medication administered to children from 0 to 7.5 years in the Avon Longitudinal Study of Parents and Children (ALSPAC).
      ], and adolescents [
      • Hansen E.H.
      • Holstein B.E.
      • Due P.
      • Currie C.E.
      International survey of self-reported medicine use among adolescents.
      ,
      • Holstein B.E.
      • Andersen A.
      • Krølner R.
      • et al.
      Young adolescents' use of medicine for headache: Sources of supply, availability and accessibility at home.
      ]. The same can be observed in Brazil. According to Moraes et al [
      • Moraes A.C.
      • Delaporte T.R.
      • Molena-Fernandes C.A.
      • Falcão M.C.
      Factors associated with medicine use and self medication are different in adolescents.
      ], in the city of Maringá, Brazil, 56% of the adolescents aged 14–18 years had used medicines in the previous 15 days; 53% used these medicines by self-medication, and the majority of these adolescents did not know the names of their medicines. Studies carried out in the city of Pelotas, Brazil, showed a high prevalence of medicine use among children and adolescents; 64% in children aged 1 year [
      • Oliveira E.A.
      • Bertoldi A.D.
      • Domingues M.R.
      • et al.
      Medicine use from birth to age two years: The 2004 Pelotas (Brazil) birth cohort study.
      ], 56% in those aged 3–4 years [
      • Béria J.U.
      • Victora C.G.
      • Barros F.C.
      • et al.
      Epidemiology of drug consumption in children of a urban center of the southern region of Brazil [in Portuguese].
      ], and 31% in those aged 11 years [
      • Bertoldi A.D.
      • Tavares N.U.
      • Hallal P.C.
      • et al.
      Medicine use among adolescents: The 11-year follow-up of the 1993 Pelotas (Brazil) birth cohort study.
      ]. Consistently, the literature indicates that the prevalence is higher among girls than boys [
      • Holstein B.E.
      • Andersen A.
      • Krølner R.
      • et al.
      Young adolescents' use of medicine for headache: Sources of supply, availability and accessibility at home.
      ,
      • Moraes A.C.
      • Delaporte T.R.
      • Molena-Fernandes C.A.
      • Falcão M.C.
      Factors associated with medicine use and self medication are different in adolescents.
      ,
      • Gobina I.
      • Välimaa R.
      • Tynjälä J.
      • et al.
      The medicine use and corresponding subjective health complaints among adolescents, a cross-national survey.
      ,
      • da Silva C.H.
      • Giugliani E.R.
      Consumption of medicines among adolescent students: A concern [in Portuguese].
      ].
      Worldwide, self-medication is an important public health problem among children and adolescents [
      • Headley J.
      • Northstone K.
      Medication administered to children from 0 to 7.5 years in the Avon Longitudinal Study of Parents and Children (ALSPAC).
      ,
      • Pereira F.S.
      • Bucaretchi F.
      • Stephan C.
      • Cordeiro R.
      Self-medication in children and adolescents.
      ]. The prevalence of self-medication among children aged 0–17 years was studied in Germany [
      • Du Y.
      • Knopf H.
      Self-medication among children and adolescents in Germany: Results of the National Health Survey for Children and Adolescents (KiGGS).
      ]. It was found that 25.2% of participants had self-medicated in the previous week, corresponding to 38.5% of total medicine use, including all pharmacological classes. Holstein et al [
      • Holstein B.E.
      • Holme Hansen E.
      • Due P.
      • et al.
      Self-reported medicine use among 11- to 15-year-old girls and boys in Denmark 1988-1998.
      ] described the self-reported medicine use for common health complaints among those aged 11–15 years in Denmark between 1988 and 1998, finding a high proportion of medicine use, and concluded that the proportion of users increased during the 10 years studied. Studies conducted in Brazil found that approximately one-half of medication use in adolescents is by self-medication [
      • da Silva C.H.
      • Giugliani E.R.
      Consumption of medicines among adolescent students: A concern [in Portuguese].
      ,
      • Pereira F.S.
      • Bucaretchi F.
      • Stephan C.
      • Cordeiro R.
      Self-medication in children and adolescents.
      ,
      • Holstein B.E.
      • Holme Hansen E.
      • Due P.
      • et al.
      Self-reported medicine use among 11- to 15-year-old girls and boys in Denmark 1988-1998.
      ]. Also, it was observed that self-medication increased according to age from 11% at 3 months to 34% at 2 years [
      • Oliveira E.A.
      • Bertoldi A.D.
      • Domingues M.R.
      • et al.
      Medicine use from birth to age two years: The 2004 Pelotas (Brazil) birth cohort study.
      ]. Among those aged 7–18 years, the risk of self-medication was twofold higher compared with children aged <7 years (odds ratio [OR] = 2.81; 95% confidence interval [CI]: 2.09–3.77) [
      • Pereira F.S.
      • Bucaretchi F.
      • Stephan C.
      • Cordeiro R.
      Self-medication in children and adolescents.
      ].
      Analyses targeted to observe the likelihood of medicine use in certain period of life in relation to medicine use in previous periods (tracking of medicine use) were not found in the literature. Tracking is defined as the stability of a variable over a period [
      • Twisk J.W.
      • Kemper H.C.
      • Mellenbergh G.J.
      Mathematical and analytical aspects of tracking.
      ,
      • Kelder S.H.
      • Perry C.L.
      • Klepp K.I.
      • Lytle L.L.
      Longitudinal tracking of adolescent smoking, physical activity, and food choice behaviors.
      ]. Malina [
      • Malina R.M.
      Physical activity and fitness: Pathways from childhood to adulthood.
      ] defined the tracking effect as “individual trend in maintaining oneself in a determined position or group after a period of time.” There are several studies in the literature that track other variables, such as food intake [
      • Boulton T.J.
      • Magarey A.M.
      • Cockington R.A.
      Tracking of serum lipids and dietary energy, fat and calcium intake from 1 to 15 years.
      ,
      • Resnicow K.
      • Smith M.
      • Baranowski T.
      • et al.
      2-year tracking of children's fruit and vegetable intake.
      ,
      • Wang Y.
      • Bentley M.E.
      • Zhai F.
      • Popkin B.M.
      Tracking of dietary intake patterns of Chinese from childhood to adolescence over a six-year follow-up period.
      ] and physical activity practice along one's life [
      • Azevedo M.R.
      • Araújo C.L.
      • Cozzensa da Silva M.
      • Hallal P.C.
      Tracking of physical activity from adolescence to adulthood: A population-based study.
      ]. In the area of pharmacoepidemiology, however, most cohort studies used cross-sectional approaches to evaluate medicine use [
      • Sturkenboom M.C.
      • Verhamme K.M.
      • Nicolosi A.
      • et al.
      Drug use in children: Cohort study in three European countries.
      ,
      • Headley J.
      • Northstone K.
      Medication administered to children from 0 to 7.5 years in the Avon Longitudinal Study of Parents and Children (ALSPAC).
      ,
      • Bertoldi A.D.
      • Tavares N.U.
      • Hallal P.C.
      • et al.
      Medicine use among adolescents: The 11-year follow-up of the 1993 Pelotas (Brazil) birth cohort study.
      ,
      • Holstein B.E.
      • Holme Hansen E.
      • Due P.
      • et al.
      Self-reported medicine use among 11- to 15-year-old girls and boys in Denmark 1988-1998.
      ], and just a few used repeated cross-sectional designs to evaluate the use of specific groups of medicines over time [
      • Liberman J.N.
      • Berger J.E.
      • Lewis M.
      Prevalence of antihypertensive, antidiabetic, and dyslipidemic prescription medication use among children and adolescents.
      ,
      • Rushton J.L.
      • Whitmire J.T.
      Pediatric stimulant and selective serotonin reuptake inhibitor prescription trends: 1992 to 1998.
      ,
      • Zito J.M.
      • Safer D.J.
      • dosReis S.
      • et al.
      Trends in the prescribing of psychotropic medications to preschoolers.
      ,
      • Zoëga H.
      • Baldursson G.
      • Hrafnkelsson B.
      • et al.
      Psychotropic drug use among Icelandic children: A nationwide population-based study.
      ]. The aim of this study was to track the use of medicine and self-medication practices from infancy to adolescence in a Southern Brazilian city.

      Methods

      All hospital births in the city of Pelotas, Brazil, in 1993 were monitored. Information was collected using a questionnaire administered by trained interviewers to mothers. In total, 5,265 mothers gave birth in that calendar year in the city, of which 5,249 agreed to take part in the cohort study. Newborns were weighed and measured. Subsamples of the cohort were visited at 1, 3, and 6 months and at 1 and 4 years of age. In each of these visits, information on medicine use by the infant/child in the 15 days before the interview was collected from mothers. At 11 and 15 years of age, all cohort members were searched for follow-up visits; again, data regarding medicine use in the 15 days before the interview were collected from mothers. For reported medicine use, mothers were asked for the name of the medicine, the reason for its use, and whether it had been prescribed by a physician. The sample size of each visit is presented in Table 1. The methodological details of the 1993 Birth Cohort Study are described elsewhere [
      • Victora C.G.
      • Hallal P.C.
      • Araújo C.L.
      • et al.
      Cohort profile: The 1993 Pelotas (Brazil) birth cohort study.
      ].
      Table 1Medicine use and self-medication among boys and girls 15 days before the interview in infancy, childhood, and adolescence—1993 Pelotas (Brazil) Birth Cohort Study
      Follow-up visitN
      Only the 11- and 15-year follow-up studies included the entire sample.
      Medicine useSelf-medication
      All (%)Boys (%)Girls (%)pAll (%)Boys (%)Girls (%)p
      1 month64964.767.461.9.14629.030.527.3.364
      3 months64468.669.967.3.48225.924.427.6.359
      6 months1,41356.654.658.4.14715.113.916.9.044
      1 year1,36252.053.550.6.30017.015.818.1.235
      4 years1,27235.037.432.7.07915.715.416.0.787
      11 years4,42630.930.231.6.32612.410.314.5<.001
      15 years4,34137.231.942.3<.00120.217.322.9<.001
      a Only the 11- and 15-year follow-up studies included the entire sample.
      For this study, we analyzed two outcomes in each of the follow-up visits: (a) prevalence of medicine use and (b) prevalence of self-medication. Self-medication refers to the use of any medicine without a medical prescription. In terms of confounders, we adjusted our analyses for sex, maternal schooling, and family income. For analyses using adolescent data, confounders were maternal schooling and family's assets index collected in adolescence.
      We carried out descriptive, crude, and multivariate analyses using Stata 10.0 (Stata Corp., College Station, TX). Analyses using variables collected at 1 and 4 years of age were weighed owing to the oversampling of low-birth-weight children. The descriptive analysis included calculating absolute numbers and percentages for all outcomes, for the whole sample, and separately for boys and girls. As the main objective was to show tracking of medicine use and self-medication, we also presented the prevalence of the outcomes according to the same variable in the previous visit. In these cases, the medicine use at 11 years of age, for example, is both an outcome (the main exposure is medicine use at 4 years of age) and an exposure (the outcome is medicine use at 15 years of age).
      In the crude analysis, the prevalence of each outcome was regressed using information on medicine use (or self-medication) in the previous visit as the main exposure. These analyses were carried out using logistic regression model, and ORs and 95% CIs are provided. For the adjusted analyses, the following variables were added to the model: sex, maternal schooling, and family income or assets index. Statistical significance was tested using the χ2 test and was set at 5% (all tests were two-tailed).
      The study was approved by the Research Ethics Committee of the School of Medicine of the Federal University of Pelotas. Parents or guardians provided written informed consent, authorizing the participation of their child in the study.

      Results

      Table 1 shows the prevalence of medicine use in children from the 1993 Birth Cohort Study. In the first year of life, the prevalence was higher (ranging from 52.0% to 68.6%) than from 4 to 15 years of age, in which the prevalence decreased (range: 30.9%–37.2%). Up to age 11, differences in medicine use by sex were not found. At age 15, girls presented a 33% higher prevalence in the use of medicine than boys.
      The prevalence of self-medication presented a U-shaped relationship with age. Prevalence values were higher in early life (up to 3 months of age) and at mid-adolescence (15 of age) as compared with late infancy (6 and 12 months of age), mid childhood (4 of age), and early adolescence (11 years of age). Self-medication tended to be higher among girls than boys in most visits, although differences were only statistically significant in adolescence (11- and 15-year follow-ups).
      Table 2 shows the prevalence of medicine use according to the frequency of medicine use in the previous follow-up visit. In all studied periods, the prevalence of medicine use was higher among children who used medicines in the earlier period. Considering medicine use in children aged 1 month, 74.6% of them also used medicines at 3 months, whereas 57.5% of those who did not use medicines at the first month of life, used them at 3 months. The same interpretation is applied to the other periods. Crude and adjusted ORs are also shown in Table 2, indicating the increased chance of medicine use in the current study in relation to the previous study. All p values were significant, indicating that previous use of medicine predicts use in the future. In the adjusted model, children who used medicines in the first month of life presented a 2.11 times higher likelihood of using medicines at 3 months of age than those who did not use at 1 month of age (OR: 2.11; 95% CI: 1.49–2.99).
      Table 2Tracking of medicine use from 1 month to 15 years of age—1993 Pelotas (Brazil) Birth Cohort Study
      Follow-up visitMedicine use in the previous follow-up visitUnadjusted
      Unadjusted: In these analyses, medicine use in each study was compared with medicine use in the previous period. For example, at 3 months, children who used medicines at the first month of life had a chance to use medicine 2.17-fold higher than children who did not use medicine at the first month.
      Adjusted
      Adjusted: Analyses adjusted for sex, maternal schooling, and family income at the time of the birth to studies from 3 months to 4 years. For 11- and 15-year follow-up visits, analyses were adjusted for sex (perinatal data), maternal education at 15 years and asset index at 11 and 15 years.
      No (%)Yes (%)OR (95% CI)pOR (95% CI)p
      3 months
      The 3-month study was compared with the 1-month study.
      57.574.62.17 (1.54–3.07)<.0012.11 (1.49–2.99)<.001
      6 months49.562.51.70 (1.21–2.39).0021.80 (1.28–2.55).001
      1 year44.457.81.72 (1.38–2.14)<.0011.73 (1.39–2.16)<.001
      4 years30.139.51.52 (1.20–1.92)<.0011.45 (1.15–1.84).002
      11 years29.137.41.45 (1.13–1.88).0041.39 (1.06–1.84).017
      15 years32.447.81.91 (1.67–2.18)<.0011.92 (1.68–2.22)<.001
      CI = confidence interval; OR = odds ratio.
      a Unadjusted: In these analyses, medicine use in each study was compared with medicine use in the previous period. For example, at 3 months, children who used medicines at the first month of life had a chance to use medicine 2.17-fold higher than children who did not use medicine at the first month.
      b Adjusted: Analyses adjusted for sex, maternal schooling, and family income at the time of the birth to studies from 3 months to 4 years. For 11- and 15-year follow-up visits, analyses were adjusted for sex (perinatal data), maternal education at 15 years and asset index at 11 and 15 years.
      c The 3-month study was compared with the 1-month study.
      Similarly, Table 3 shows the same analyses using self-medication as the outcome. Prevalence of self-medication was higher among those who were self-medicated in the previous periods than those who did not self-medicate. However, in two follow-up visits (1 and 11 years of age), the difference was not statistically significant.
      Table 3Tracking of self-medication from 1 month to 15 years of age—1993 Pelotas (Brazil) Birth Cohort Study
      Follow-up visitSelf-medication in the previous follow-up visitUnadjusted
      Unadjusted: In these analyses, self-medication in each study was compared with self-medication in the previous period.
      Adjusted
      Adjusted: Analyses adjusted for sex, maternal education, and family income at the time of the birth to studies from 3 months to 4 years. For 11- and 15-year follow-up visits, analyses were adjusted for sex (perinatal data), maternal education at 15 years and asset index at 11 and 15 years.
      No (%)Yes (%)OR (95% CI)pOR (95% CI)p
      3 months
      The 3-month study was compared with the 1-month study.
      20.539.32.50 (1.75–3.63)<.0012.34 (1.60–3.42)<.001
      6 months13.129.82.82 (1.83–4.34)<.0013.02 (1.94–4.72)<.001
      1 year16.421.31.38 (.95–2.01).0861.40 (.97–2.04).075
      4 years14.721.01.54 (1.06–2.23).0241.50 (1.03–2.19).035
      11 years13.017.71.44 (.95–2.19).0881.40 (.90–2.19).140
      15 years19.128.21.67 (1.35–2.05)<.0011.62 (1.31–2.02)<.001
      a Unadjusted: In these analyses, self-medication in each study was compared with self-medication in the previous period.
      b Adjusted: Analyses adjusted for sex, maternal education, and family income at the time of the birth to studies from 3 months to 4 years. For 11- and 15-year follow-up visits, analyses were adjusted for sex (perinatal data), maternal education at 15 years and asset index at 11 and 15 years.
      c The 3-month study was compared with the 1-month study.

      Discussion

      The purpose of evaluating tracking of medicine use from childhood to adolescence is to identify the increased risk of overmedication and to carry out preventive action aimed at increasing the rational use of medicines during this developmental period in life. Considering that adolescence is a developmental stage with special concerns related to behaviors and needs regarding health care, it is important to understand medicine use in this period. Longitudinal analyses carried out using data from birth cohort studies are the ideal source of information on this issue.
      In the present study, those who used medicines in the previous period were consistently more likely to use medicines in the following visits, regardless of age, income, and maternal education. The proportion of medicine use among those who had previously used medicines was higher than among those who did not use medicines before, thus one of the most important contributions of this article was to demonstrate that there is a tracking of medicine use from childhood to adolescence. A tracking effect was also observed in the practice of self-medication; those who self-medicated in the past were more likely to continue to do so.
      Cohort studies conducted with children and adolescents in the northern region of the Netherlands in 1998 [
      • Schirm E.
      • van den Berg P.
      • Gebben H.
      • et al.
      Drug use of children in the community assessed through pharmacy dispensing data.
      ], in Denmark between 1988 and 1998 [
      • Holstein B.E.
      • Holme Hansen E.
      • Due P.
      • et al.
      Self-reported medicine use among 11- to 15-year-old girls and boys in Denmark 1988-1998.
      ], and in the city of Pelotas, Brazil [
      • Bertoldi A.D.
      • Tavares N.U.
      • Hallal P.C.
      • et al.
      Medicine use among adolescents: The 11-year follow-up of the 1993 Pelotas (Brazil) birth cohort study.
      ], assessed the prevalence of medicine use at different ages. However, these studies used cross-sectional analyses, and therefore did not track the use of medicine over time.
      The prevalence of medicine use was higher in the first year of life and decreased with age until the beginning of adolescence, where a small increase was observed, as found in previous international [
      • Schirm E.
      • van den Berg P.
      • Gebben H.
      • et al.
      Drug use of children in the community assessed through pharmacy dispensing data.
      ] and national studies [
      • Bertoldi A.D.
      • de Barros A.J.
      • Wagner A.
      • et al.
      Medicine access and utilization in a population covered by primary health care in Brazil.
      ]. In a cohort study performed in the northern region of the Netherlands, Schirm et al [
      • Schirm E.
      • van den Berg P.
      • Gebben H.
      • et al.
      Drug use of children in the community assessed through pharmacy dispensing data.
      ] reported that the prevalence of medicine use in children aged 1 year was 87%; this prevalence decreased to 51% until 12 years of age, remained stable at around 50% from 6 to 12 years of age, and increased to 64% at 16 years of age.
      Bertoldi et al [
      • Bertoldi A.D.
      • de Barros A.J.
      • Wagner A.
      • et al.
      Medicine access and utilization in a population covered by primary health care in Brazil.
      ] conducted a study in Southern Brazil that included individuals between 0 and 19 years of age living in an area covered by the Family Health Program (Programa de Saúde da Família, PSF). Results of this study found the prevalence of medicine use to be higher in those aged 0–4 years (50.6%), to decrease in children aged 5–9 years (35.2%), and to increase again in those aged 10–19 years (38.7%).
      The present study is consistent with the national [
      • Moraes A.C.
      • Delaporte T.R.
      • Molena-Fernandes C.A.
      • Falcão M.C.
      Factors associated with medicine use and self medication are different in adolescents.
      ,
      • da Silva C.H.
      • Giugliani E.R.
      Consumption of medicines among adolescent students: A concern [in Portuguese].
      ] and international [
      • Hansen E.H.
      • Holstein B.E.
      • Due P.
      • Currie C.E.
      International survey of self-reported medicine use among adolescents.
      ,
      • Holstein B.E.
      • Andersen A.
      • Krølner R.
      • et al.
      Young adolescents' use of medicine for headache: Sources of supply, availability and accessibility at home.
      ,
      • Gobina I.
      • Välimaa R.
      • Tynjälä J.
      • et al.
      The medicine use and corresponding subjective health complaints among adolescents, a cross-national survey.
      ] literature regarding the increased use of medicine during adolescence, in which there is evidence of differences by sex in adolescents, with girls having a higher prevalence of medicines use than boys [
      • Hansen E.H.
      • Holstein B.E.
      • Due P.
      • Currie C.E.
      International survey of self-reported medicine use among adolescents.
      ,
      • Holstein B.E.
      • Andersen A.
      • Krølner R.
      • et al.
      Young adolescents' use of medicine for headache: Sources of supply, availability and accessibility at home.
      ,
      • Moraes A.C.
      • Delaporte T.R.
      • Molena-Fernandes C.A.
      • Falcão M.C.
      Factors associated with medicine use and self medication are different in adolescents.
      ,
      • Gobina I.
      • Välimaa R.
      • Tynjälä J.
      • et al.
      The medicine use and corresponding subjective health complaints among adolescents, a cross-national survey.
      ,
      • da Silva C.H.
      • Giugliani E.R.
      Consumption of medicines among adolescent students: A concern [in Portuguese].
      ].
      The prevalence of medicines used at 15 years of age was higher than the prevalence at 11 years of age; these prevalence rates are lower than those found in other studies (40%–56%) with teenagers [
      • Hansen E.H.
      • Holstein B.E.
      • Due P.
      • Currie C.E.
      International survey of self-reported medicine use among adolescents.
      ,
      • Holstein B.E.
      • Andersen A.
      • Krølner R.
      • et al.
      Young adolescents' use of medicine for headache: Sources of supply, availability and accessibility at home.
      ,
      • Moraes A.C.
      • Delaporte T.R.
      • Molena-Fernandes C.A.
      • Falcão M.C.
      Factors associated with medicine use and self medication are different in adolescents.
      ,
      • Gobina I.
      • Välimaa R.
      • Tynjälä J.
      • et al.
      The medicine use and corresponding subjective health complaints among adolescents, a cross-national survey.
      ,
      • da Silva C.H.
      • Giugliani E.R.
      Consumption of medicines among adolescent students: A concern [in Portuguese].
      ]. The trend of increasing use with age during adolescence is similar to findings from other studies. However, to make comparisons between studies, considerations must be given to the variability in the recall period and the ages of the participants in each study.
      Holstein et al [
      • Holstein B.E.
      • Andersen A.
      • Krølner R.
      • et al.
      Young adolescents' use of medicine for headache: Sources of supply, availability and accessibility at home.
      ] conducted research with students aged 11–13 years in six European countries and asked about medicine use for headaches in the past month. The results indicate that 42.5% of the sample had used medicines for headaches during the past month, and this prevalence increased with age and in girls.
      Gobina et al [
      • Gobina I.
      • Välimaa R.
      • Tynjälä J.
      • et al.
      The medicine use and corresponding subjective health complaints among adolescents, a cross-national survey.
      ] studied adolescents aged 11–15 years and medicines used by them for headaches, stomachaches, inability to sleep, and nervousness for a period of 1 month in 19 countries in Europe and in the United States. On average, the most prevalent use of medicine was for headaches (40.9%), followed by stomachaches (23.8%). This study also reported increased medicine use according to age and higher prevalence in girls, for all medicines examined.
      De Moraes et al [
      • Moraes A.C.
      • Delaporte T.R.
      • Molena-Fernandes C.A.
      • Falcão M.C.
      Factors associated with medicine use and self medication are different in adolescents.
      ] evaluated the prevalence of medicine use in the past 15 days among high school students (14–18 years old) living in an urban area in Southern Brazil in 2007. This study found 55.8% of adolescents took medicine, and the rate was also higher in girls (girls = 64.3%, boys = 45.7%, p < .001). Age presented a positive and significant linear trend (p = .0001), with the prevalence rate increasing from 50% in those aged 14 years to 57.6% in those aged 16 years.
      Furthermore, a study conducted with a representative sample of schoolchildren aged 14–16 years, in Porto Alegre, Southern Brazil, found the consumption of medicine in the past 7 days was 49.5%, with a significantly higher proportion of girls using medicine than boys (57.6% vs. 38.8%, p = .001). The same type of upward trend according to age was also observed in this study [
      • da Silva C.H.
      • Giugliani E.R.
      Consumption of medicines among adolescent students: A concern [in Portuguese].
      ].
      As for self-medication, the data confirm that this is a fairly common practice among children and adolescents. The prevalence of self-medication was higher in the first 3 months of life, decreasing to values around 15% until 11 years of age, and at 15 years of age, there was an increase, driven primarily by an increase in self-medication in girls. The difference between sexes in self-medication was evident and has been demonstrated by other authors [
      • Hansen E.H.
      • Holstein B.E.
      • Due P.
      • Currie C.E.
      International survey of self-reported medicine use among adolescents.
      ,
      • Du Y.
      • Knopf H.
      Self-medication among children and adolescents in Germany: Results of the National Health Survey for Children and Adolescents (KiGGS).
      ,
      • Carrasco-Garrido P.
      • Hernández-Barrera V.
      • López de Andrés A.
      • et al.
      Sex-differences on self-medication in Spain.
      ]. In a study by Hansen et al [
      • Hansen E.H.
      • Holstein B.E.
      • Due P.
      • Currie C.E.
      International survey of self-reported medicine use among adolescents.
      ], at 11 and 15 years of age, a statistical significant difference was shown among girls and boys in self-medication. Yong Du and Hildtraud Knopf [
      • Du Y.
      • Knopf H.
      Self-medication among children and adolescents in Germany: Results of the National Health Survey for Children and Adolescents (KiGGS).
      ] studied self-medication during the previous week among children and adolescents from 0 to 17 years of age in Germany. The authors found that 25.2% of participants had used self-medication. As in the present study, overall, girls showed a significantly higher level of self-medication than boys, and self-medication increased from 14 to 17 years of age.
      The increased use of medicines and self-medication by girls at 15 and 11 years of age, respectively, may be explained by menarche, a period in which girls use analgesics and contraceptives. Hansen et al [
      • Hansen E.H.
      • Holstein B.E.
      • Due P.
      • Currie C.E.
      International survey of self-reported medicine use among adolescents.
      ] showed that for girls aged 11–15 years, use of medicines for headaches and stomachaches occurred more often than among boys [
      • Hansen E.H.
      • Holstein B.E.
      • Due P.
      • Currie C.E.
      International survey of self-reported medicine use among adolescents.
      ]. Dysmenorrhea is associated with younger age [
      • Ohde S.
      • Tokuda Y.
      • Takahashi O.
      • et al.
      Dysmenorrhea among Japanese women.
      ], and dysmenorrheal women use numerous drugs by self-medication for pain but infrequently accessed formal medical care [
      • Ortiz M.I.
      • Fernández-Martínez E.
      • Pérez-Hernández N.
      • et al.
      Patterns of prescription and self-medication for treating primary dysmenorrhea in a Mexican population.
      ]. Another explanation is that women typically present greater readiness to acknowledge and express their health needs as compared with men, thus also presenting higher use of medical care [
      • Marcell A.V.
      • Klein J.D.
      • Fischer I.
      • et al.
      Male adolescent use of health care services: Where are the boys?.
      ]. The study by Klein et al reinforces this idea by showing that the proportion of girls who reported using a physician's office was significantly higher than boys [
      • Klein J.D.
      • Wilson K.M.
      • McNulty M.
      • et al.
      Access to medical care for adolescents: Results from the 1997 Commonwealth Fund Survey of the Health of Adolescent Girls.
      ]. According to Marcell et al, in younger adolescents (11–15 years old), there are no differences between the sexes regarding health care visits; however, in older male subjects, these visits are significantly reduced in comparison with female subjects [
      • Marcell A.V.
      • Klein J.D.
      • Fischer I.
      • et al.
      Male adolescent use of health care services: Where are the boys?.
      ].
      In a study by Abahussain et al [
      • Abahussain E.
      • Matowe L.K.
      • Nicholls P.J.
      Self-reported medication use among adolescents in Kuwait.
      ], performed in Kuwait, the prevalence of self-medication among adolescents aged 14–19 years was high (92%), increasing with age from 87% among those aged 14 years to 95% among those aged 18 years; 65% of medicines used were for pain relief. In Brazil, studies show that the prevalence of self-medication in adolescents is approximately 30% [
      • Pereira F.S.
      • Bucaretchi F.
      • Stephan C.
      • Cordeiro R.
      Self-medication in children and adolescents.
      ,
      • Silva I.M.
      • Catrib A.M.
      • de Matos V.C.
      • Gondim A.P.
      Self-medication in adolescence: A challenge to health education [in Portuguese].
      ]. In a study by Silva et al [
      • Silva I.M.
      • Catrib A.M.
      • de Matos V.C.
      • Gondim A.P.
      Self-medication in adolescence: A challenge to health education [in Portuguese].
      ], conducted in Fortaleza, Ceará, Brazil, with adolescents aged 13–18 years, 34% reported ever having used medicines because of media advertisements.
      According to Silva et al [
      • Silva I.M.
      • Catrib A.M.
      • de Matos V.C.
      • Gondim A.P.
      Self-medication in adolescence: A challenge to health education [in Portuguese].
      ], teenagers are in a phase of life in which they are formulating views on various social factors, including the use of medicine and other substances. The authors point out the widespread practice of self-medication in adolescence, particularly among girls, envisioning possible permanent medicine users.
      Usually in childhood, and often in adolescence, the person who provides the medicine to the child is either the mother or guardian responsible for them. In a study conducted among adolescents [
      • da Silva C.H.
      • Giugliani E.R.
      Consumption of medicines among adolescent students: A concern [in Portuguese].
      ], one predictor of high medication use in children and adolescents was maternal education. Lower maternal educational was associated with greater likelihood of self-medication. Bertoldi et al [
      • Bertoldi A.D.
      • Tavares N.U.
      • Hallal P.C.
      • et al.
      Medicine use among adolescents: The 11-year follow-up of the 1993 Pelotas (Brazil) birth cohort study.
      ] found that medicine use was directly associated with economic status and maternal schooling and reported 28% higher levels of self-medication in groups with more household assets and higher maternal schooling [
      • Bertoldi A.D.
      • Tavares N.U.
      • Hallal P.C.
      • et al.
      Medicine use among adolescents: The 11-year follow-up of the 1993 Pelotas (Brazil) birth cohort study.
      ]. The same study reported a positive association between maternal use of hypnotic drugs and sedatives and adolescent medicine use.
      One of the limitations of tracking studies is how to conduct the tracking analysis. Tracking is often estimated by correlation coefficients between two continuous variables collected at different time points or by the proportion of subjects consistently classified in a certain “risk” group at a follow-up measurement. Also, ORs are used to estimate the magnitude of tracking [
      • Twisk J.W.
      • Kemper H.C.
      • Mellenbergh G.J.
      Mathematical and analytical aspects of tracking.
      ]. In addition to this broader limitation, there are specific limitations to the self-report of medicine use and self-medication owing to the likelihood of recall bias. Another problem is the possibility that some mothers were unaware of the use of medicines by the adolescents, particularly contraceptives, as well as medicines used in the treatment of sexually transmitted diseases, for example.
      Tracking studies are important from an epidemiological perspective because future behavior may be “predicted” by analyzing the past, thus aiding in the design of preventive actions. In our study, we showed that both medicine use and self-medication track over time. In addition to the tracking effect, the prevalence of medicine use and self-medication was high. Educational programs about safe and rational use of medicines at school level targeted to students and their relatives could be a strategy to prevent abusive use of medicines and irresponsible self-medication. Future studies will benefit from analyzing tracking of use of specific pharmacological groups.

      Acknowledgments

      The cohort study is supported by the Wellcome Trust. The initial phases of the cohort were funded by the European Union and the Brazilian National Program for Centers of Excellence (PRONEX), National Research Council (CNPq), and the Ministry of Health.

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