Secondary consequences of ADHD are the difficulties that build up when ADHD goes unidentified or unsupported, such as anxiety, low self-esteem, job loss or debt.
They are called secondary because they follow from living with ADHD in settings that weren't designed for it, rather than being part of ADHD itself. Years of missed deadlines, lost jobs and being told to try harder affect how a person sees themselves.
Common ones include anxiety, depression, low self-esteem, strain in relationships, money problems and using alcohol or other substances to manage feelings. Many adults come to assessment with a long list of these and no explanation for any of them.
This is one of the strongest reasons to get assessed as an adult. A diagnosis does not undo the past. It can change how you understand it, and support for the ADHD itself can ease the secondary difficulties over time.