Why do treatments have conflicting effects in comorbidity? 

When ADHD occurs alongside depression or bipolar disorder, treatment can become more complicated. According to the NHS, each condition affects brain chemistry differently, so medication that benefits one may worsen symptoms of another. For example, stimulants used for ADHD can sometimes heighten anxiety or trigger mood swings in people with bipolar disorder, while antidepressants may offer little benefit for ADHD symptoms. This makes sequencing, careful monitoring, and specialist supervision essential in comorbid treatment. 

How comorbidity influences treatment response 

The NICE ADHD guideline (NG87, 2025) and NICE bipolar disorder guidance (CG185, 2025) both emphasise the need for a staged approach when managing overlapping conditions. Clinicians are advised to stabilise mood symptoms, particularly in bipolar disorder, before introducing stimulants such as methylphenidate. NICE also notes that atomoxetine may be preferred when anxiety or depression are significant, as it carries a lower risk of mood destabilisation. The NHS England ADHD Taskforce (2025) supports this, recommending multidisciplinary reviews and long-term monitoring for those with complex comorbid presentations. 

Biological and pharmacological factors 

According to recent PubMed reviews, the reason treatments sometimes conflict lies in overlapping neurochemical systems. Dopamine and norepinephrine imbalances drive ADHD, while serotonin pathways dominate in depression. Stimulants that increase dopamine may unintentionally heighten emotional reactivity, whereas antidepressants acting on serotonin can fail to address ADHD-related inattention or impulsivity. This biological overlap explains why some individuals experience improvement, while others see symptom worsening or unexpected side effects. 

Managing comorbid ADHD and mood disorders safely 

The Royal College of Psychiatrists advises gradual medication titration, collaborative planning, and integrated therapy when treating comorbid ADHD and mood disorders. Research published on PubMed found that stimulant use alongside mood stabilisers is generally safe once bipolar symptoms are controlled, but starting stimulants before mood stabilisation increases the risk of relapse or manic episodes. NHS guidance also highlights that regular reassessment helps reduce adverse outcomes and supports sustained recovery. 

Key takeaway 

Comorbidity alters how treatments work because ADHD, depression, and bipolar disorder involve different but overlapping brain systems. As both NICE and the NHS stress, managing such cases requires careful sequencing, frequent review, and multidisciplinary collaboration. Stabilising mood first, introducing ADHD medication gradually, and maintaining regular monitoring can help ensure safer and more effective outcomes for people living with both conditions. 

Harriet Winslow, BSc

Author

Harriet Winslow is a clinical psychologist with a Bachelor’s in Clinical Psychology and extensive experience in behaviour therapy and developmental disorders. She has worked with children and adolescents with ADHD, autism spectrum disorder (ASD), learning disabilities, and behavioural challenges, providing individual and group therapy using evidence-based approaches such as CBT and DBT. Dr. Winslow has developed and implemented personalised treatment plans, conducted formal and informal assessments, and delivered crisis intervention for clients in need of urgent mental health care. Her expertise spans assessment, treatment planning, and behavioural intervention for both neurodevelopmental and mental health conditions.

All qualifications and professional experience stated above are authentic and verified by our editorial team. However, pseudonym and image likeness are used to protect the author's privacy.

Dr. Rebecca Fernandez, MBBS

Reviewer

Dr. Rebecca Fernandez is a UK-trained physician with an MBBS and experience in general surgery, cardiology, internal medicine, gynecology, intensive care, and emergency medicine. She has managed critically ill patients, stabilised acute trauma cases, and provided comprehensive inpatient and outpatient care. In psychiatry, Dr. Fernandez has worked with psychotic, mood, anxiety, and substance use disorders, applying evidence-based approaches such as CBT, ACT, and mindfulness-based therapies. Her skills span patient assessment, treatment planning, and the integration of digital health solutions to support mental well-being.

All qualifications and professional experience stated above are authentic and verified by our editorial team. However, pseudonym and image likeness are used to protect the reviewer's privacy.