It is not easy to establish whether a person has ADD or not. The presence of 9 symptoms characterizes the disorder, but 6 is sufficient for clinical diagnosis of ADD. Even with 6 symptoms, it is then not always straightforward to distinguish the attention deficit disorder from mania or depression.
The symptoms may increase and decrease in severity, as well. The instability of the disorder may encourage doctors to overdiagnose it and therefore to overprescribe stimulant drugs to treat it.