What is Dual Diagnosis?

Dual diagnosis refers to simultaneously experiencing an intellectual or developmental disability (IDD) along with a mental health condition. IDD may encompass physical or cognitive limitations that impact essential life activities, while mental health disorders can involve medical, environmental, emotional, or psychiatric factors.

Intellectual disability and developmental disability are often referred to together using the IDD acronym. Intellectual disability involves a notable limitation in intellectual functioning and adaptive behavior that manifests before the age of 18 and is a type of developmental disability. On the other hand, a developmental disability is a disability that arises during the developmental stage and may or may not involve intellectual limitations (Lineberry et al., 2023). Research shows that individuals with IDD have higher rates of mental health conditions compared to those without IDD (Lin et al., 2021, Lineberry et al., 2023) potentially up to four times more likely than the general population (Cooper et al., 2007).

People with IDD and co-occurring mental health conditions are often under-diagnosed, untreated, or inappropriately diagnosed because symptoms of mental illness often present differently in individuals with IDD. The process of accurately diagnosing psychiatric conditions becomes increasingly challenging as intellectual functioning decreases (Hsieh et al., 2020). Referrals to a psychiatrist are commonly made for individuals exhibiting self-harm, aggression, impulsivity, hyperactivity, or significant changes in behavior.