Are you distinguishing between dependency and addiction here? I know you typed dependence, but it can be quite a separate thing from addiction, which most experts will agree IS a disease. Most addicts are dependant on a drug or medication (meaning the body needs it to function as it has been), but addiction involves the maladaptive behaviors that are considered a disease, such as over-indulgence, drug seeking, thinking about the substance constantly and how to obtain more, etc. On the other hand, a person in chronic pain may be dependant on an opiate drug simply because they've taken it for a long time, but not be addicted (they don't misuse the drug, or think about it 24/7 except for the purpose of relieving pain).
Addiction is a disease, while dependency might not necessarily be so. Is that your position you're debating, or are you wanting to argue that addiction is not a brain disease (in which case, I don't think I can help you, because I believe that it is... but someone else on the site might).