A research study from the The Lundbeck Foundation Initiative for Integrative Psychiatric Research iPSYCH shows that people with ADHD, who also have another psychiatric diagnosis, are more likely to stop taking their ADHD medicine...According to research, although stimulants work for the majority of people with ADHD, the medications sometimes can cause side effects, and up to fifty per cent stop taking their ADHD medications within two years of beginning the treatment.