Having ADHD is an independent risk factor for several common serious mental health issues including major depression and anorexia, researchers have concluded.
The neurodevelopmental condition was also found to be associated with risk of suicide and post-traumatic stress disorder, the German study published in BMJ Mental Health found.
But there was no evidence for a causal link between ADHD and bipolar disorder, anxiety, or schizophrenia, the results of the analysis which used Mendelian randomisation to look at how genetic variants associated with the conditions were linked.
The detailed analysis which used several techniques to test the associations found that genetic liability to ADHD was independently associated with the risk of anorexia nervosa (28%).
And it showed that ADHD both caused (9% heightened risk), and was caused by (76% heightened risk), major clinical depression.
After adjusting for the influence of major depression, a direct causal association with both suicide attempt (30% heightened risk) and PTSD (18% heightened risk) emerged, the researchers found.
It builds on data from observational studies which has linked ADHD has been linked to mood and anxiety disorders, they explained.
The same gene may be associated with different traits, making it difficult to pinpoint the relevant causal effect and only people of European ancestry were included so the findings might not apply to other ethnicities, they pointed out.
But the findings should encourage clinicians to be more proactive when treating people with ADHD, they concluded, with the study providing a guide to the mental comorbidities on which to focus.
Diagnoses of ADHD in the UK have been rising with figures published in July showing that more adults than children were prescribed drugs to treat the condition for the first time.
In 2022/23 prescribing of medicines for ADHD increased by 32% in adults and 12% in children under the age of 17, the data shows.
‘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 Dr Dennis Freuer from the University of Augsberg.
He added: ‘There is little doubt that ADHD and other mental disorders share common pathophysiological causes, but the exact causative mechanisms have not yet been fully elucidated.
‘A further important issue in this connection is that children with ADHD are often treated with psychostimulant drugs which could have an effect on the development of further mental disorders later in life.’