Berg Xaver1, Colla Michael1, Seifritz Erich1, Claussen Malte Christian1,2,3
1 Department of Psychiatry, Psychotherapy and Psychosomatics, University Hospital of Psychiatry Zurich, Zurich, Switzerland
2 Private Clinic Wyss AG, Münchenbuchsee, Switzerland
3 Psychiatric Services Grisons, Chur, Switzerland
Attention Deficit Hyperactivity Disorder (ADHD) is a common neurodevelopmental disorder which is characterized by symptoms of inattention, hyperactivity, and impulsivity. The estimated prevalence of ADHD in the general population is 7,2% in children, with persistence into adulthood of approximately 35%. [1,2]
Although there is a lack of population studies, the postulated prevalence of ADHD in young athletes ranges from 4,2 to 8,1%, suggesting ADHD could be more common in athletes compared to the general population.  The reasons for a presumably higher prevalence of ADHD among athletes could be, among other things, that the influence of the sporting activity leads to better well-being of the potential patients and therefore becomes a central part of their lifestyle. A further reason could be that intensive physical activity can have a beneficial effect on the comorbid symptoms of ADHD. [4,5] People with ADHD may, therefore, benefit more from physical activity than people without ADHD, and maybe attracted to physical activity for this reason.  Adolescents with ADHD may also be more attracted to sports activities than to academic activities because of their inherent motor restlessness and possible negative feedback in class due to disruptive behavior.  Besides, some research has shown that athletes and individuals with ADHD have specific traits that are shared by both groups, such as novelty-seeking behavior and reward dependency. 
The clinical course of ADHD is associated with a variety of different impairments and can lead to mental, social, educational, and professional impairments. Athletes with ADHD may also suffer from a loss of performance due to comorbid disorders (e.g., affective disorders, anxiety, drug abuse), a significantly increased and socially unaccepted impulsiveness, and reduced self-esteem. [9,10] Besides those negative consequences of ADHD, athletes with ADHD can also use their elevated impulsivity as a resource, allowing them to make quick and unpredictable decisions, reportedly losing this trait under ADHD treatment. [11,12]
The treatment of ADHD in adults includes different treatment strategies, which can be divided into behavioral and pharmaceutical interventions. While the former does not underlie restrictions in the care of athletes, there are essential considerations to be made about the latter: Medications can be divided into two classes, Stimulants (Amphetamine, Methylphenidate and its derivates) and Non-Stimulants. First-line treatment of adult ADHD according to NICE and other national guidelines are stimulants (namely Methylphenidate and Lisdexamfetamine). Switching to Non-Stimulants (Atomoxetine, Guanfacine, Atypical Antipsychotics) is recommended in case of insufficient symptom response despite having used adequate doses of stimulants or if the patient does not tolerate medication with stimulants. From a clinical point of view, the effect strengths of stimulants are slightly higher than those of Non-Stimulants.
While stimulants, in general, are effective and well-tolerated, there are specific limitations when used by athletes: The World Anti-Doping Agency (WADA) lists stimulant medication as prohibited in-competition, which means athletes who are under treatment need to have a therapeutic use exemption (TUE). WADA bans stimulants because they can be misused for performance enhancement. If taken before physical activity, stimulants can cause an “ergogenic effect”, which leads to an increase of muscular strength, running speed, acceleration, and anaerobic capacity. [13,14,15] Athletes using stimulants could, therefore, gain an unfair advantage over athletes who do not use these substances. Some experts, therefore, recommend that stimulants should not be used by athletes. 
Besides the distortion of competition, there are specific side effects of stimulants, which raised concern about the dangerous consequences of use, mainly sudden cardiac death (SCD) and heat illness. SCD is a frequently reported cause of death in athletes.  Stimulants can cause cardiovascular side effects (e.g., the elevation of heart rate and blood pressure) and have therefore been suspected of causing an increased risk of SCD. However, to this date, no evidence of correlation of ADHD medications and sudden cardiac death has been shown. [18,19] Heat illness is caused by increased heat production of the body and impaired dissipation of heat. Ultimately it can lead to heatstroke, which is the third most common cause of death in athletes. [7,20] It has been shown that in warm environments, Amphetamines can lead to higher physical performance and higher body temperature without the athlete experiencing more stress while exercising.  Therefore, an increased risk of heat illness caused by stimulants seems possible, but further research is warranted.
Management of ADHD in athletes remains controversial. We think it is necessary to conduct population studies among athletes first to provide more accurate prevalence rates. To contribute to this, we are planning a cohort study consisting of 2 phases: At phase one, we will screen undiagnosed athletes for symptoms of ADHD and typical comorbidities by using questionnaires. At phase 2, we will invite those study participants with striking scores and test them for ADHD by structured clinical interviews. We will also compare their results with a healthy control group of athletes. This way, we hope to be able to get reliable data on the prevalence of ADHD in athletes.
In the longitudinal course, the described cohort study could be followed by further research on the effects of long-lasting stimulants on the physical performance of athletes with ADHD, because previous studies focused mainly on short-lasting stimulants and healthy individuals. We hope to use this research to develop therapeutic strategies that address the specific needs of top athletes and improve the emotional state of athletes.
Dr. med. Xaver Berg
Department of Psychiatry,
Psychotherapy and Psychosomatics,
University Hospital of Psychiatry Zurich,
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