Cross-addiction and cross-dependence are synonymous terms used to describe a condition in which an individual is addicted to more than one substance. Different substances often affect the brain in similar manners. Those suffering from addiction are likely to be dependent on these similarly acting substances, which include heroin and other opiates, alcohol, and tranquilizers.
According to Recovery Today Online, cross-addiction is caused because the motivation to repeat certain behaviors is reinforced by the release of the chemical dopamine in the pleasure center of the brain. The release of dopamine causes sensations of pleasure and relaxation in the individual. Although each class of drugs affects an individual area of the pleasure center, all of them follow a similar nerve pathway that leads to the release of dopamine. One of the reasons for cross-addiction is the activation of this common pathway.
Cross-addiction is significant for individuals in recovery because often a relapse is caused by the use of a substance that is not the addict's drug of choice, particularly a drug that affects the pleasure center in a similar fashion. For example, someone recovering from alcohol addiction may be prescribed medication in good faith for treating a condition such as anxiety or insomnia, but that may lead to addictive use of the prescription medication and eventually to using the drug of choice again.