All addictions work in the same parts of the brain, by modifying or imitating the production of neurotransmitters that cause pleasant feelings. This is as true of shopping addiction as it is of heroin. Thus, people who have taught themselves that their moods and feelings can be altered by certain actions or chemicals, have a very good chance of cross-addiction to chemicals and actions that have similar effects. Gambling, for example, is the number two substitute addiction for alcoholics and addicts, after relationships.
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. Alcohol and benzodiazepine tranquilizers are one example. Heroin and other opioid drugs are another, as are alcohol and heroin.
Cross addiction and cross dependence are the same thing, really. “Cross dependence” is just a way of saying it that makes it sound less important. Thus the term is much favored by drug companies.