Prevalence of methylphenidate use among adolescents in Ontario

ABSTRACT

Despite a growing interest in the use of methylphenidate (Ritalin) to treat attention deficit/hyperactivity disorders, prevalence data has been scarce in Canada. A probability school survey conducted in 1997 among Ontario students in grades 7, 9, 11 mid 13 is used to collect data on such use. Overall, 3.4% of students (5.3% of males, 1.7% of females) used methylphenidate in the previous year. Rates and patterns are similar to those found in the United States. Future research needs to examine reasons and correlates of use, extent of medical supervision and possible non-medical use of methylphenidate.

ABREGE

En depit d'un int@ret croissant pour l'usage du methylphenidate (Ritalin) dans le traitement des troubles d'hyperactivite avec deficit de l'attention (THDA), les donnees sur sa prevalence sont rares au Canada. Nous recueillons des donnees sur cet usage par le biais d'une enquete probabiliste menee en 1997 dans les ecoles aupres d'eleves ontariens inscrits en 7', 9, llr et 13, annees. Dans l'ensemble, 3,4 % des eleves (5,3 % des garcons et 1,7 % des filles) ont fait usage de methylphenidate durant l'annee precedence. Les tendances et les taux observes au Canada sons semblables a ceux observes aux EtatsUnis. Des recherches plus poussees devraient etablir des correlations entre l'usage, l'ampleur de la supervision medicale et le potential d'usage non medical du methylphenidate.

Although methylphenidate has been intensely studied and widely used as a treatment for Attention Deficit/Hyperactivity Disorders (ADHD) for approximately 30 years,' the drug is still a subject of controversy. In the United States, use of methylphenidate rose steadily between 1971 and 1987.2 A subsequent wave of negative publicity and lawsuits involving Ritalin' appears to have caused a significant decline in the use of the drug to treat hyperactivity and inattentiveness between 1989 and 1991.' More recent data suggests that methylphenidate use is increasing once again in the 1990s.5',

There may be a number of potential problems linked to such an increase which should be a cause for some concern. One obvious question is whether the prevalence of ADHD is actually increasing, or is methylphenidate being prescribed to children and adolescents who do not really need it? The very concept of ADHD has undergone numerous changes through the years,' so it is possible that a wider range of symptoms has led to a wider use of methylphenidate. For instance, one notable change has been the distinction between Attention Deficit Disorder with and without hyperactivity.2 Students who are inattentive, but not necessarily hyperactive are now more likely to be treated with stimulants than in the past. A related issue is whether the increasing number of students receiving methylphenidate are also receiving the psychological, social or educational treatment which is often critical for successfully treating ADHD. Recent surveys of pediatricians suggest that this may not be the case; methylphenidate is often the sole treatment for patients with ADHD.8'9 Given increases in methylphenidate use, adverse side effects due to methylphenidate may also increase. While methylphenidate is generally considered a relatively safe stimulant,I a surprising number of adverse side-effects have been noted in the literature,10 the prevalence of which may become more common if methylphenidate is inappropriately prescribed or if the patient lacks proper supervision. An additional concern is that the increase in prescribed use will allow more of the drug to be diverted for non-medical use among various subpopulations including other children, adults and drug use addicts." Various clinical studies have found serious consequences of methylphenidate abuse, including morbidity and mortality that is similar to, or exceeds that of cocaine and amphetamines.,13

Despite the fact that methylphenidate use has become an important public health issue, reliable prevalence estimates have been scarce.' Data for elementary and secondary students, the most common users of methylphenidate, has been especially absent. Past reports of prevalence estimates have relied on a number of methods. One approach is to use the prevalence of ADHD as a proxy to estimate the drug prevalence, since roughly 90% are likely to be treated with methylphenidate.5' For example, the Ontario Child Health Study reported rates of hyperactivity for boys and girls aged 4-16 to be 8.9% and 3.3%, respectively." In the United States, one potentially alarming indicator of rising prevalence was the 6-fold increase in methylphenidate production since 1990." In response to these reports, Safer and colleagues used a variety of data sources to estimate trends in methylphenidate use in the United States, including repeated surveys of school nurses, pharmaceutical databases and physician surveys, and found much more modest increases.5 Overall, they estimate that approximately 2.8% of youths in the United States used methylphenidate in 1995.

Surprisingly, self-report student surveys have not been used for collecting data on methylphenidate use. In the United States, large-scale student drug use surveys such as Monitoring the Future ask about illicit drugs only." Although past student drug use surveys in Canada have asked about the use of medical drugs, including stimulants, they have not included specific questions about Ritalin.16,17 It is doubtful whether such questions are useful as indicators of methylphenidate use, given that they combine all stimulants and presuppose that students could correctly classify a drug which reduces inattention and hyperactivity as a stimulant. Furthermore, doctors prescribing stimulant medication typically tell patients not the name of the drug, but that the drug will allow them to concentrate, calm them or assist them with schoolwork.9

The aim of this study is to present prevalence and population estimates of methylphenidate use among Ontario students based on a self-report drug use survey. As far as we are aware, this is the first time in Canada that data on methylphenidate has been collected from a large-scale probability survey of youth.

METHOD

We use data from the 1997 cycle of the Ontario Student Drug Use Survey, 18 a cross-sectional probability survey of Ontario students enrolled in grades 7, 9, 11 and 13 (ages 10 to 20 years). Because the OSDUS is a biennially-repeated monitoring survey, it provides a timely vehicle to address various public health issues among adolescents, such as in this case, the self-reported use of methylphenidate. The OSDUS, administered by the Institute for Social Research, York University, employs a single-stage cluster probability design stratified proportionately into four geographical regions (Toronto, West, East and North Ontario) and equally within the four grades. In total, 3,990 students from 22 school boards, 168 schools and 234 classes comprise the final sample. The overall student participation rate is 77%. Further details of the study design are available."' All analyses are conducted with Stata 5.0 using the svy procedure in order to properly account for the stratification and clustering of the survey design.'9

We ask students two questions concerning Ritalin use. The first is a measure of 12-month prevalence: "Sometimes doctors give medicines such as Ritalin to students who are hyperactive or have difficulties concentrating in school. This is sometimes called Attention Deficit Disorder. During the last 12 months, have you taken any medicine like Ritalin that was prescribed by a doctor?" The response categories are either yes or no. Although this question cannot directly determine the prevalence of prescribed medication for ADHD, it can provide useful bounds in establishing the magnitude of methylphenidate usage. The question specifically mentions Ritalin, since it is the most well-known name, but is also general enough to include other drugs which may be used to treat ADHD. The second question is a measure of the duration of current daily Ritalin use: "If you have used Ritalin within the last two days, how long have you been using it daily?" Although regular use does not necessarily imply daily use, since methylphenidate may not be prescribed on weekends or summer months, we consider daily use to be a reasonable indication of typical Ritalin use. A detailed study of duration would require many more questions, but we were restricted to one question due to time constraints. The response categories include: never in my lifetime; I have used Ritalin but not in the last 12 months; less than 1 month; daily for I to 6 months; daily for 7 to 12 months; daily for I to 2 years; daily for 3 to 4 years; and daily for more than 4 years. Because of the small number of current daily users, we collapse the last six categories into 1 to 12 months, 1 to 4 years and more than 4 years.

We present prevalence estimates and 95% present prevalence intervals for the total sand 95% confidence intervals for the total as by sex, grade and region. In addition, as well as by sex, grade and region estimates are further dition, all grade and region estimated by sex, given the confurther disaggregated by sex, given finding that males are much more likely to receive stent finding that males.5 In addition more prevalence estimates, we include stimulants.5 In addition to prevalence estimates for the include popul and males and tion estimates for the total and males. Finally, we include data on the females. Finally, we include data on of daily Ritalin use. duration of daily Ritalin use.

As seen in Table I, the prevalence of past 12 months' Ritalin use among Ontario students is 3.4% (2.6% to 4.2%, 95% CI), an estimate within the range of the 2.8% found in the United States in 1995.5 Despite differences in study design and population, rates of Ritalin use for males (5.3%) and females (1.7%) are also consistent with, although somewhat lower than, the prevalence of hyperactivity in Ontario among 12 to 16 year old males (7.3%) and females (3.4%).14 Our data likely underestimate the prevalence of methylphenidate use, given that our sample includes students 18 and older and we do not include special schools in our sample, so students with the most serious learning disabilities would be excluded. The prevalence rates for males and females also reflect the narrowing of the traditional sex differences. We find a 1:3 female/male ratio, a figure consistent with recent reports from the United States which range from 1:5 to 1:2.5. 5. Projecting our prevalence rates to the population of grades 7, 9, 11 and 13 students, we estimate that approximately 16,187 students (11,835 males and 4,352 females) used methylphenidate in the previous 12 months.

Our data show a clear decrease in methylphenidate use by grade (Table II). Use is highest among Grade 7 students (5.1%) and declines to 1.5% for Grade 13 students. Similarly, use among males declines from 8.6% to 1.7%. However, rates among females only vary between 1 and 2%. It should be noted that younger students not included in our sample would likely have much higher prevalence rates than the Grade 7 students. Medication for ADHD is typically most common by grade three and declines thereafter.' Differences by region, however, are much less pronounced. Estimates range from 2.7% to 4.0% among the total sample, 3.8% to 5.6% among males, and 1.6% to 2.6% among females. Lastly, the duration of daily Ritalin use is shown in Table III. Overall, 5.3% of students used Ritalin in their lifetime. Lifetime, but not past 12 months use is 3.1 %, higher than all the current daily users (2.3%).

DISCUSSION

The lack of prevalence data for methylphenidate use among students in Canada makes it difficult to put the current findings into context. In addition, our sample does not include special schools or younger grades where methylphenidate tends to be more prevalent. Also, since this is the first time we included methylphenidate in our survey, we have no trend data with which to compare it. Unlike the United States, which has data going back to the 1970s, we have no way of knowing whether our current estimates for Ontario are higher or lower than in the past. Still, there are enough similarities to the recent US data to suggest that the situation in Ontario may be comparable to that in the United States and that our data provide reasonable estimates of methylphenidate use. Both the total prevalence rate and the female-male ratios are close to recent US figures.

Our results also support the use of selfreport drug use surveys as a means of collecting and monitoring data on methylphenidate. Alternative methods, such as production quotas, prescription databases or physician surveys often are not practical, have serious limitations or provide only limited data. The advantage to the self-report survey is that it also allows the opportunity to investigate a wide range of social, behavioural and demographic variables and their relationships to methylphenidate use.

In addition to studies of prevalence and incidence of use, a number of important research topics involving methylphenidate need to be addressed. One issue is whether students who are being treated with methylphenidate for ADHD are also receiving complementary non-drug care such as behavioural treatments, educational care or psychological counselling, and whether such a multimodal approach is more effective than drug treatment alone. School surveys could also be used to examine whether students using methylphenidate differ from their peers on such variables as educational attainment, mental health or illicit drug use. One last emerging issue especially suited to the survey approach is that of non-medical use of methylphenidate. As the drug becomes more popular, there have been numerous anecdotal reports of students sharing, stealing and buying methylphenidate for their own non-medical use.20 It would be valuable to obtain more rigorous and systematic evidence of such diversion before it becomes a potential public health issue.

[Reference]

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Received: November 30, 1998 Accepted: May 31, 1999

[Author Affiliation]

Frank.J. Ivis, BA, Edward M. Adlaf, phDI,2

[Author Affiliation]

1. Centre for Addiction and Mental Health

2. Department of Public Health Sciences, Faculty of Medicine, University of Toronto Correspondence and reprint requests: Edward M. Adlaf, Centre for Addiction and Mental Health, 33 Russell Street, Toronto, Ontario, MSS 2S1, Tel: 416-595-6925, Fax: 416-595-6899, E-mail: eadlaf@arf.org