“Going Through Life on Hard Mode”—The Experience of Late Diagnosis of Autism and/or ADHD: A Qualitative Study Blandine French 1,2 and Sarah Cassidy 2 Abstract Background: In the United Kingdom, more than 2.5 million adults with undiagnosed neurodevelopmental conditions, such as autism and attention-deficit/hyperactivity disorder (ADHD), can face difficulties accessing diagnosis and support. Our qualitative study explores people’s experiences of receiving a diagnosis in adulthood and its impact on their lives. Methods: We conducted semi-structured interviews with seven health care professionals and 13 late-diagnosed adults (5 autistic, 5 with ADHD, and 3 with dual diagnoses) using reflexive thematic analysis. Results: We developed five themes from the analysis representing the journey and factors influencing participants’ experiences of receiving a late diagnosis: (1) the key role of relationships and mental well-being; (2) the wider impact on well-being and lifelong mental health; (3) understanding—the answer to postdiagnosis changes; (4) the flip side of diagnosis—the burden of a label; and (5) are you ready—the importance of timing. Conclusion: Our study demonstrates the multiple impacts a lack of diagnosis has and the many benefits experienced from receiving one. Although a lack of diagnosis can at times have some negative effects, the importance of understanding and the wider impacts on relationships and mental well-being are discussed. Primarily, the emerging concept of being ready and the importance of the right timing highlight an important nuance in the diagnosis journey. Keywords: ADHD, Autism, diagnosis impact, interviews, experiences Community Brief Why is this an important issue? In the United Kingdom, more than 2.5 million adults with undiagnosed neurodevelopmental conditions such as autism and ADHD often struggle to access diagnosis and support. What was the purpose of this study? This study aimed to explore the experiences of adults receiving a diagnosis of autism or ADHD later in life and how the lack of diagnosis affected them. What did the researchers do? The research involved interviews with 7 health care professionals and 13 late-diagnosed adults (5 with autism, 5 with ADHD, and 3 with both conditions). We conducted these interviews over Teams and included representa- tions from different countries, conditions, and genders to ensure we represented a wide range of experiences. 1 Academic Unit of Mental Health & Clinical Neurosciences, School of Medicine, Institute of Mental Health, University of Nottingham, Nottingham, United Kingdom. 2 School of Psychology, University of Nottingham, Nottingham, United Kingdom. 1 AUTISM IN ADULTHOOD Volume 00, Number 00, 2024 ª Mary Ann Liebert, Inc. DOI: 10.1089/aut.2024.0085 Open camera or QR reader and scan code to access this article and other resources online. Downloaded by Amy Pearson from www.liebertpub.com at 07/26/24. For personal use only.