Attention-deficit/hyperactivity disorder (ADHD) is a neurodevelopmental condition in children and teens that extends into adulthood in up to around two thirds of cases. Worldwide, its prevalence is estimated to be around 5 per cent in children/teenagers and 2.5 per cent in adults.
ADHD has been linked to mood and anxiety disorders in observational studies, but it’s not known if it’s causally associated with other mental ill health.


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Researchers from the University of Augsburg in Germany found evidence for a causal link with a heightened risk of anorexia nervosa (28 per cent), and evidence that ADHD both caused (9 per cent heightened risk), and was caused by (76 per cent heightened risk), major clinical depression. 
And after adjusting for the influence of major depression, a direct causal association with both suicide attempt (30 per cent heightened risk) and PTSD (18 per cent heightened risk) emerged.


The team recommended vigilance by health professionals in a bid to ward off these disorders later on.


“This study opens new insights into the paths between psychiatric disorders. Thus, in clinical practice, patients with ADHD should be monitored for the psychiatric disorders included in this study and preventive measures should be initiated if necessary,” said the team in the paper published in the open access journal BMJ Mental Health.  


In the study, the researchers used Mendelian randomisation, a technique that uses genetic variants as proxies for a particular risk factor -- in this case ADHD -- to obtain genetic evidence in support of a particular outcome -- in this study, 7 common mental health issues.


These were: major clinical depression; bipolar disorder; anxiety disorder; schizophrenia; post traumatic stress disorder (PTSD); anorexia nervosa; and at least one suicide attempt.


The researchers initially used the technique to establish potential links between ADHD and the seven disorders. They then used it to see if disorders associated with ADHD could potentially be responsible for the effects detected in the first analysis. Finally, they pooled the data from both analyses to calculate the direct and indirect effects of ADHD.
 
There was no evidence for a causal link between ADHD and bipolar disorder, anxiety, or schizophrenia, the results of the analysis showed.