Cross addiction and cross dependence are the same thing. “Cross dependence” is just a way of making addiction sound less unpleasant. Thus, the term is much favored by drug companies, who generally prefer to soft-pedal the more unsavory facts about their products.
All addictions work in the same parts of the brain, by modifying the production of, or imitating the action of the brain chemicals that cause pleasant feelings — our built-in reward system. This is as true of things like shopping as it is of heroin. Over a period of time, our brains change so that they then require the extra stimulation that the drug or activity provides, and they don’t especially care where it comes from. At that point, we may discover other ways to deal with our discomfort that quickly satisfy the craving and become addictions in their own right.
People who have taught themselves that their moods and feelings can be altered or suppressed by certain activities or chemicals have a very good chance of cross-addiction to things that have similar effects. Relationships and gambling, for example, are common substitute addictions for alcoholics and other addicts. The mere fact of addiction predisposes us to other comfort-seeking behavior.
This poses a definite hazard to people in recovery. When we get clean and sober, or begin to deal with other dependencies, our discomfort may lead to our looking for mood-altering activities. We run a great risk of quick addiction to the substitute.
In a slightly different sense, the actions of some chemicals are so similar that a person addicted to one will almost automatically become addicted to the other after a very short period of use. Alcohol and tranquilizers are one example, and there are many others. Just using these similar drugs, even if we never become dependent on them, recreates the conditions in our brains that can — and usually do — lead us quickly back to our drugs of choice.
These are the reasons that we believe recovery requires abstinence from all mood altering, whether by chemicals or activities that distract us from our purpose. There is plenty of time to explore the world outside of addiction, but we first need to understand the risks as well as the rewards.