Many people with conditions such as depression and ADD self medicate that much is true. DG was diagnosed ADD as opposed to ADHD. We covered this in an earlier thread. Those conditions are commonly lumped into one category but there are significant differences. The H stands for hyperactivity and DG was not diagnosed as hyperactive. ADD people also often self medicate with alcohol, nicotine, marijuana and even comfort food but they are usually polar opposites to the hyperactive ADHD. While many people of high intellect are ADD in fact, ADD has nothing to do with intelligence or determination. ADHD and ADD are neurobehavioral disorders caused by alterations in brain chemicals and changes in the way the brain works. They both present unique challenges, but don't have to get in the way of success. Many successful people have managed the condition. Albert Einstein is said to have had symptoms of ADD.
http://en.wikipedia.org/wiki/History_of_attention_deficit_hyperactivity_disorder
BBM
The DSM-II (1968) began to call it "Hyperkinetic Reaction of Childhood" even though the professionals were aware that many of the children so diagnosed exhibited attention deficits without any signs of hyperactivity. In 1980, the DSM-III introduced the term "ADD (Attention-Deficit Disorder) with or without hyperactivity." That terminology (ADD) technically expired with the revision in 1987 to ADHD in the DSM-III-R. In the DSM-IV, published in 1994, ADHD with sub-types was presented. The current version (as of 2008), the DSM-IV-TR was released in 2000, primarily to correct factual errors and make changes to reflect recent research; ADHD was largely unchanged.[2]
Under the DSM-IV, there are three ADHD sub-types, including one which lacks the hyperactivity component.[9] Approximately one-third of people with ADHD have the predominantly inattentive type (ADHD-I), meaning that they do not have the hyperactive or overactive behavior components of the other ADHD subtypes.
Even today, the ADHD terminology is objectionable to many. There is some preference for using the ADHD-I, ADD, and AADD terminology when describing individuals lacking the hyperactivity component, especially among older adolescents and adults who find the term "hyperactive" inaccurate, inappropriate and even derogatory.
Basically the terms have been interchangeable for a long time now.