An addictive substance is a non-essential element, meaning it is not necessary to maintain or sustain life. These chemicals can impact the nervous system by producing a sensation of satisfaction as it creates the desire (craving) and need (physiological dependency) for more of the element. Using the element repeatedly will result in a changed nervous system that now defines the element as being necessary for life, as essential as oxygen, food, water, shelter, and relationships. Eventually, the value of this element surpasses all the other ingredients, and the addicted individual will be willing to sacrifice any of the other elements to get more of the addictive substance.