In economics, neutral goods are goods whose demand is independent of income. Such goods have substitution effects but not income effects. Examples of neutral goods include prescription medicines for people with medical conditions, such as insulin for diabetics. Although an individual's income may vary, their consumption of vital prescription medicines will remain constant. This means demand for these goods is perfectly inelastic; the income effect equals the substitution effect. Arguably illicit drugs would fit into this category as anecdotally poor addicts will go to great lengths such as prostitution, theft and robbery to gain the income to pay for their addiction.