Parkinson’s disease, characterized by tremor, rigidity and slowness of movement, mood disorders, daytime sleepiness and a host of other symptoms both movement-related and non-movement-related occurs when brain cells that make the neurotransmitter dopamine, die for unknown or “idiopathic” reasons. There’s a region of the brainstem called the Substantia Nigra where most of these dopamine neurons live. By the time movement symptoms occur in idiopathic Parkinson’s disease as many as 80 percent of these neurons have died. Many environmental chemicals like pesticides have been implicated as possible initiators in this mysterious death process however recent studies suggest that ADD (attention-deficit disorder) therapy with amphetamine stimulants might be another initiator of Substantia Nigra cell death in Parkinson’s; probably through a mechanism known as excitotoxicity.
For many years, roughly 5 decades, amphetamine stimulant compounds have been increasingly prescribed for children diagnosed with ADD (attention deficit disorder) and ADHD (attention deficit hyperactivity disorder). Adults receiving prescriptions for ADD have also increased in number in recent decades. The prevailing wisdom has been that although illegal use of amphetamine stimulants for recreation has been shown to lead to “excitotoxicity” of brain cells, its controlled prescribed use in ADD and ADHD is relatively safe because the doses are controlled and titrated to improve cognition without causing the excess stimulation or “high” experienced by recreational users.
Studies on rodents and primates show this class of drugs causing elevated levels of the stimulant neurotransmitter chemical glutamine, especially around areas that control movement and motivation/emotional excitement: the basal ganglia and limbic system respectively. Further, prolonged exposure leads to a loss in markers for the neurotransmitters serotonin (related to mood and depression) and dopamine. Further, studies in rodents have shown significant cell loss in the upper brainstem, close to the very area where the dopamine-neuron-rich Substantia Nigra region sits. This is all theoretical and nonclinical and thus has never stirred prescribing caregivers into worrying about whether ADD or ADHD patients might develop Parkinson’s down the road.
Recently however a large epidemiological study conducted in California has yielded some very disturbing possible conclusions on the issue of the safety of prescribed amphetamine stimulants. The study questioned 64 thousand volunteers on their use if any, of prescribed amphetamines for weight loss. Subjects who reported prescribed amphetamine use had a 60 percent increased incidence of Parkinson’s disease over those who reported no amphetamine use. Although the study’s authors caution that further research needs to be done there is certainly a statistical correlation. Correlation is not causation however given the theoretical risks discussed above, this study may open the door to a flood of follow up studies implicating prescribed use of these drugs as being less safe than originally thought. One needs to wait and see. However this author would hope that the results produce a sense of caution in the ADD/ADHD stimulant-prescriber community and among educational professionals who have taken a rather routine view in referring children with ADD/ADHD suggestive profiles to such prescribing professionals.