Here are seven questions or factors we need to address to assess the validity of studies on ADHD stimulant medications and their effects on growth:
Is there a history of prior stimulant medication use? Surprisingly, a number of studies on the inhibitory effects of ADHD stimulant medications either neglect or downplay the fact that children in their studies had a previous history of stimulant medication usage for their conditions. This can seriously confound effects, for if a child was taking a stimulant medication previously, he or she may still be on track for a lower baseline growth rate. Furthermore, if a child was taken off stimulant medications recently, there remains the possibility that his or her system is beginning to play "catch-up" by displaying a greater-than-normal increase in growth following a medication "holiday". In either case, baseline readings are skewed, and these effects muddy the accuracy of current stimulant medication studies on growth effects. Poulton and Nanan make this observation in their article on prior treatments with stimulant medication and growth in children with ADHD. They go on to say that growth is an accurate indicator of prior treatment with stimulant medication.
Beware of the pretreatment bias with regards to effectiveness of stimulant medications:Poulton and Nanan also warned about the natural bias of individuals with a previous treatment history of stimulants in that they have already proven to have a greater tolerance to potential side effects (otherwise they would have likely discontinued earlier stimulant treatments) and an overall higher levels of compliance and positive response to stimulant medications. This too, can give a potential "false positive" with regards to evaluating the effectiveness of current stimulant medication treatments for ADHD.
Do untreated children and adolescents with ADHD have different growth patterns than non-affected children? This is also a much-neglected consideration. Spencer and coworkers performed a study in which they saw a slower growth rate in the earlier years for children with ADHD, which was followed by a significantly later "catch" up period. In other words, compared to non-ADHD children, individuals with ADHD may be more predisposed to being "late bloomers", even when they are unmedicated. This potential difference in growth patterns between ADHD'ers and non-ADHD'ers, while still highly debatable, should at least raise the question as to whether delays in growth patterns for medicated individuals with ADHD can actually be attributed to the medications or to the nature of the disorder itself (or a combination of both).
Do "drug holidays" work? This is actually comprised of several questions and considerations. It is not uncommon for parents or prescribing physicians to allow for "drug holidays" for unmedicated ADHD children. These holidays can vary from a few days to longer periods such as an entire summer vacation. If the period of these drug holidays is long enough, such as in a summer-long study by Gittleman-Klein and coworkers on methylphenidate and growth, significant changes may be seen. This study saw a relative increase in weight but not in height following a summer off of medication of the stimulant methylphenidate (Ritalin). Of potential interest was the observation that following a second holiday from medication the following summer, a relative increase in height but not in weight was observed. It is entirely possible that the duration and frequency of drug holidays may effect the two parameters (height and weight) in slightly different fashions. Another article by Poulton suggests the possibility that height gains may take longer to remedy because gains in weight may drive subsequent growth in height.
Are the growth changes due to stimulant medication temporary or permanent? Although hotly debatable, it appears that growth impairments due to prescribed stimulant medication usage is more of a short-term effect. A follow-up study of medicated ADHD children into adulthood indicated that even at moderately-high doses of the stimulant medication methylphenidate (45 mg/day average), medicated children with ADHD eventually reached normal final heights when compared to controls. It is worth mentioning, however, that these children eventually discontinued their medications. It is unclear as to what the effects may have been had they continued on with the methylphenidate usage into adulthood (especially since there has been a sharp trend towards continuing stimulant medication treatment into adulthood for adult ADHD).
In reference to point number 3. My son has ADHD (diagnosis at age 4 years). At age almost 15 years he has yet to start puberty and has been diagnosed with consitutional delay. The endocrinologist pointed out that he sees this 'often' in children with ADHD. After much research I recognised the pattern in my child which the paediatrician I saw when he was an infant failed to recognise. He was born a normal healthy weight (9 pounds 1oz) but at around 3 months stopped gaining weight until he dropped to about the 10th percentile where he has stayed until hitting around 12 where his peers again took a big leap forward and he didn't. When I expressed my concerns with the paediatrician I was told that he was just finding where he is supposed to be. If I had been told that this was an indication that he might have consititutional delay then I would have been more pro-active and possibly prevented my son from the depression that has now engulfed him. Other research suggests that the ADHD child's brain matures approx. 2 years after those of their peers. I hate to think that medication which helps so many children survive and excel at school and at home could be blamed for causing growth delays. Clearly a lot more research needs to be done to help our children.