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Stimulant medication for attention deficit hyperactivity disorder (ADHD) had a negative effect on a child's ability to get to sleep and resulted in overall less sleep time, a small meta-analysis measuring the impact of stimulants on a child's sleep found.

, of the University of Nebraska in Lincoln, and colleagues, examined nine total studies. The seven studies that addressed the effect of stimulant medication on sleep latency, or time to onset of sleep, for children with ADHD found a significant and moderate adjusted effect size of 0.54 (95% CI 0.28-0.81; P<0.001).

This means that based on a Hedges' g effect size, the difference between medicated and unmedicated sleep were 0.54 standard deviations apart. These effects were defined as being in the medium range.

Frequency of medication was a significant moderator of the sleep latency effect, as every additional time the medication was given, the effect size became greater by 0.42 standard deviations, the authors reported in

In an interview with 番茄社区, Kidwell said there were so few studies included because she and her team only wanted to include randomized controlled trials or studies that used objective measures of sleep (as opposed to checklists filled out by parents about insomnia and adverse effects).

"While our study summarizes the current state of the literature, we really need more quality research," she said. "Those studies that are really delving into sleep are kind of few and far between."

Kidwell's team also looked at sleep efficiency, or the proportion of time one is actually sleeping, and found stimulant medication had a significant and small-to-moderate adjusted effect size of -0.32 standard deviations (95% CI -0.63 to -0.01; Q[6]=41.75; P<0.001).

Several moderating variables had an impact on the results. Studies using polysomnography (PSG) to assess sleep efficiency had an effect size that was more negative by 0.81 standard deviations compared with studies using actigraphy (a sensor measuring human rest/activity cycles), indicating that stimulant use was more apparent when assessed via PSG.

But increases in length of time that youth were on the medication and an increase in the number of nights that sleep was assessed resulted in less negative effect sizes of 0.05 and 0.04 standard deviations, respectively. Sex also played a role, as stimulant medication had more of an impact on boys' sleep efficiency. For every 1-percentage point increase in the proportion of male subjects in the sample, the effect size became more negative by 0.02 standard deviations, the authors wrote.

The seven studies examining the effect of stimulant medications on total sleep time for children with ADHD had similar results. There was an overall effect size of -0.59 standard deviations (95% CI -0.84 to -0.35; P<0.001; I²=82.67%) that was moderate and significant.

Kidwell said that the study provides important information about the potential "cost" of using stimulant medication to treat children with ADHD, which should be factored into a clinician's decision about whether to prescribe this type of medication for certain patients.

"We're not saying that pediatricians should not prescribe stimulants – they're really beneficial for many kids and they're generally well tolerated, but this study just provides one potential cost that should be weighed, especially for children who are already having problems with sleep," she said.

Researchers examined nine total studies with total enrollment of 246 children/adolescents with ADHD who had been randomly assigned to stimulants and objective sleep measurement (actigraphy or PSG). Studies not including information about the key variables were excluded.

Limitations to the meta-analysis include the publication bias that existed for sleep latency and sleep efficiency effect sizes, which have underestimated the impact of stimulant medication on children with ADHD. The authors also note that due to the small number of studies, the relationships between moderators and effect sizes may not be truly representative of actual relationships between the constructs and that inconsistent reporting of similar variables across studies prevented the completion of multiple regression analyses.

Kidwell would like to see more research, particularly using objective methods to measure sleep such as PSG and actigraphy (only two studies used PSG, which is considered the "gold standard" for sleep measurement).

"I think if we had those really high level, rigorous methods in place, it would shed a lot more light on what's going on with these children," she concluded.

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