November 5, 2013

expert reaction to Ritalin and addiction

A rat study in Nature Communications found the active component in Ritalin, methylphenidate, can enhance the way the brain responds to further exposure to the drug and can cause increased amphetamine-seeking behaviour.

Prof Anita Thapar, Professor of Child & Adolescent Psychiatry Section, Institute of Psychological Medicine and Clinical Neurosciences and MRC Centre for Neuropsychiatric Genetics and Genomics, Cardiff University, said:

“Extreme caution is needed before these findings can be extrapolated to human ADHD and clinical practice. ADHD is much more complex than this rat model based on one neurotransmitter.”

Prof Philip Asherson, Professor of Molecular Psychiatry at the MRC Social, Genetic and Developmental Psychiatry centre at the Institute of Psychiatry, King’s College London and consultant psychiatrist at the Maudsley Hospital, said:

“People might think this research suggests that children being treated appropriately with methylphenidate (MPH) for ADHD are at risk of addiction. In fact the paper clarifies that untreated children with ADHD might be at risk of addiction due to high dopamine transport (DAT) levels, and therefore could benefit from treatment. They also point out that when MPH is taken orally in usual therapeutic doses then there were no discernible neurochemical consequences on the dopamine system. The potential problems could, however, occur when MPH is abused by taking in high doses and taken by other methods such as injection – in other words when MPH is abused.

“Whether abusing MPH does increase risk to stimulant addiction in humans is not clear, but is suggested by this research in a rat model of the effects of injected high dose MPH. It may be that MPH when abused in this way does increase the risk of addiction, as does the abuse of other drugs such as alcohol, cocaine, amphetamine and so on. Here the authors describe a mechanism for this and make the point that MPH is not dissimilar to drugs like amphetamine and cocaine in this regard, with abuse potential. But, this is not the same as saying that children when treated appropriately for ADHD are at increased risk of addiction, and available evidence shows the opposite effect with neutral or reduced risks in those treated for ADHD.

“Further work is required to fully understand the abuse potential of MPH based on these findings and to clarify whether the risk is similar in humans to that seen in these rat models. The risks can be mitigated by the use slow release of stimulant drugs (such as MPH) that cannot be taken by injection or intranasal route. The authors suggest that measuring DAT levels might be a way to identify individuals at particular risk of addiction to stimulants but this remains speculation at this point in time.”

Prof Eric Taylor, Emeritus Professor of Child and Adolescent Psychiatry, Institute of Psychiatry, King’s college London, said:

“It is not possible to generalise directly from rats injected in the laboratory to humans being given therapy. Several prospective studies have examined whether young people taking methylphenidate to treat ADHD are more likely to abuse these or other drugs in later life; they find that the medication carries no such risk.

Refs:

Biederman et al. 2008. Stimulant therapy and risk for subsequent substance use disorders in male adults with ADHD: a naturalistic controlled 10-year follow-up study. American Journal of Psychiatry, 165(5): 597-603

Mannuzza et al. 2008.  Age of methylphenidate treatment initiation in children with ADHD and later substance abuse: prospective follow-up into adulthood.  American Journal of Psychiatry, 165(5): 604-609

Wilens  et al. Does ADHD predict substance-use disorders? A 10-year follow-up study of young adults with ADHD. Journal of the American Academy of Child and Adolescent Psychiatry, 50(6):543-553

‘Methylphenidate amplifies the potency and reinforcing effects of amphetamines by increasing dopamine transporter expression’ by Erin Calipari et al. published in Nature Communications on Tuesday 5th November.