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As a result, some parents and prescribing physicians choose a non-stimulant form of medication for treating ADHD such as Atomoxetine (Strattera). While some of the negative side effects mentioned above are less common for these non-stimulant options, the overall efficacy of reducing core ADHD symptoms is often less extensive than for the stimulant counterparts.

In this post, we will investigate one of the problem areas of stimulant medication by examining a handful of studies comparing and contrasting the different effects of methylphenidate and atomoxetine on sleep patterns in ADHD individuals. Sleep patterns are often analyzed via reports (either the patients themselves, or parents if the patient is a child), actigraphy (less invasive) or polysomnography (more details and quantitative data).

While sleep difficulties are clearly evident in several studies, numerous others have actually shown overall positive effects of methylphenidate on sleep performance. For example, a study by Boonstra and colleagues on sleep activity patterns in adult ADHD showed that methylphenidate administration resulted in a delayed period of sleep onset. However, once subjects did fall asleep, the frequency of nighttime awakenings decreased significantly for the methylphenidate group (keep in mind that all of these individuals had ADHD), and that the overall duration of sleep for the night was less for the methylphenidate participants. These positive results were echoed in a study by Sobanski and coworkers, which found that methylphenidate administration improved efficiency and restorative quality in adults with ADHD compared to non-medicated individuals with the disorder. In other words, it appears that although methylphenidate can delay the onset of sleep, it appears to offer a positive effect in promoting a deeper pattern of less-interrupted sleep in ADHD adults.

Another key issue, is the relative lack of long-term controlled studies on methylphenidate in children due to a myriad of safety and practicality issues. As a result, obtaining clear-cut and accurate information on ADHD stimulant medications and sleep disorders in children is more tenuous than in the adult model, even though the overall number of studies on ADHD medication effectiveness is much higher in children. In other words, sleep disorders still hold a relatively remote corner amongst the sea of information on pediatric ADHD.

Nevertheless, several studies on the matter have been done in the past few years. I will highlight some of them below:

An investigation by OBrien and coworkers found a significant increase in sleep disturbances for ADHD children regardless of medication status. These findings suggest a neutral effect of stimulant medications such as methylphenidate for children with ADHD, but cite an often-overlooked characteristic: ADHD children typically exhibit more sleep difficulties than non-ADHD children. Therefore, some of the bad rap attributed to ADHD stimulant medications such as methylphenidate for inducing sleep disorders may simply be due to the nature of the individuals ADHD and not to the medication. This is an important observation to keep in mind, especially when investigating sleep medication studies.

There is even some evidence that the assertion of methylphenidate administration later in the day (afternoon) may negatively impact sleep performance is less pronounced than popularly believed. Many physicians fear that a third daily dose of methylphenidate may cause sleep difficulties and omit the afternoon dosage. However, a study by Kent indicates that this may not be the case. Of course this is just one study, and should be regarded as such, but this may at least open the possibility that a number of these afternoon medication/sleep impairment fears may be less grounded than previously believed. Nevertheless, sleep disturbances are still a concern with ADHD medications such as methylphenidate, but, according to recent findings, the effects are relatively small.

This is an intriguing question which needs to be investigated further. We have had several previous discussions on the COMT gene and its effects on ADHD. Now it appears that sleep disorders and potential medication response may actually be impacted by an individual variation in this hotbed region of the human genome. A study done by Gruber and coworkers suggests that ADHD children with the Val form of the COMT gene may be more prone to sleep difficulties while on methylphenidate compared to the Met form of the COMT gene (if you are unfamilar with this "Val", "Met" and "COMT" terminology, a good explanation of these terms and how they relate to ADHD and ADHD medications can be found here).

In contrast to methylphenidate, which seems to delay the onset of sleep, individuals on atomoxetine have a much smaller delay in sleep onset. These differences were highlighted in an article by Sangal and coworkers titled Effects of Atomoxetine and methylphenidate on sleep in children with ADHD. Other advantages of atomoxetine over methylphenidate include less irritability, less difficulty getting ready for bed, less difficulty waking up in the morning, and less of an appetite suppression. However, the postive effects of fewer nighttime awakenings seen in methylphenidate were not observed in atomoxetine.

A comparison of differences between Atomoxetine (Atom) and Methylphenidate (MPH), as well as the effects of both medications compared to unmedicated ADHD individuals are shown above. Quantitative measurements were performed using both polysomnography (polysom) and actigraphy. Some key trends of note:

• A delayed onset of sleep was seen in Methylphenidate.
• However, REM sleep (an important factor in overall sleep quality) was reached faster with Methylphenidate and slower with Atomoxetine.
• Additionally, a slight increase in the percentage of sleep time spent in REM was seen with methylphenidate treatment.
• Fewer sleep disruptions (partial or full, as in awakenings) were seen with both medications, but the effects were even greater in the methylphenidate group.
• When a child did awaken during the sleep cycle, the children medicated with methylphenidate were able to fall back asleep much faster. Note this contrast to the increased time to fall asleep initially for the methylphenidate group.

Overall, it appears that while methylphenidate does slow the onset of sleep initially at a significant level, it appears that once a child does fall asleep, the overall sleep quality is actually improved if the child is medicated with methylphenidate. This data runs against the grain as far as prescription medications for ADHD are concerned, in which nonstimulants such as Strattera (Atomoxetine) are often given in favor of stimulants such as methylphenidate if sleep disorders are a concern. This is likely due to the most obvious parameter (initial difficulty falling asleep), which favors Strattera, while the other parameters, which favor methylphenidate and are more numerous, are less intrinsically obvious.

Why the pronounced difference between the two ADHD medications?

While there is still a fair amount of debate surrounding the exact cause of different impacts of these ADHD medications on sleep, the different biological targets and modes of action may offer some clues. For example, while methylphenidate primarily targets the neuro-signaling agent dopamine in brain regions such as the striatum and nucleus accumbens, Strattera (atomoxetine) instead targets another neurotransmitter called norepinephrine.

It appears that the different neurochemical targets and specific brain regions impacted by the two medications are responsible for the differences. For example, we have previously mentioned in another post on gene variations and attention control that the cingulate region of the brain, which essentially acts as the brains gear shifter, has a high density of receptors for dopamine, the very chemical that methylphenidate targets. It is possible that changes in dopamine levels from methylphenidate may indirectly impact the "gear shifting" ability of the key brain region of the cingulate. We have previously discussed that an overactive cingulate region can lead to difficulties changing focus or transitioning between topics or activities, while an underactive cingulate can lead to difficulty maintaining focus on a particular thought or state.

Putting this into context of our sleep and ADHD medication discussion, it is also worth noting that the Sangal paper mentioned that children who took the methylphenidate had a more difficult time getting up in the morning and settling down into a pre-bedtime routine than the Strattera group. In other words, it seems like the methylphenidate group had trouble with transitions. As a result, this blogger hypothesizes that the transitions may be caused, at least in part, by the increased activity of the cingulate region of the brain and its high density of dopamine targets, which see increased activities driven by a boost in free dopamine levels from the methylphenidate. In other words, I suggest the possibility that methylphenidate induces a state of the cingulate "gear" shifter becoming overactive and getting stuck in one routine (either the waking or sleeping state) and having trouble moving to another (getting out of bed or falling asleep). Further supporting this hypothesis is the data from the table above showing that the methylphenidate treatment group appears to be more inert (i.e. fewer sleep interruptions, and a quicker return to a previous sleeping state).

Compounding the problem of sleep disorders in children is the relative inconsistency between parental reports of sleep disturbances and disorders and results derived from actigraphic studies. This appears to be a recurring problem in the literature, and is confirmed by several other studies of observation. Additionally, teacher evaluations may also be flawed with regards to sleep disorders and ADHD-like behaviors.