Caffeine is a central nervous system stimulant. Caffeine is present in many commonly consumed beverages and candies and in many over-the-counter and prescription medicines, usually in combination with other chemicals, as cold and allergy tablets, headache medicines, diuretics, and stimulants. Caffeine is developmentally toxic in several species of laboratory animals. Caffeine administered to rats under several different regimens also produced subtle behavioral changes in the offspring postnatally. In the human, a number of studies have assessed the developmental toxicity potential of caffeine. While cigarette smoking was an associated factor with reduced birth weight, a subgroup among nonsmokers in the same study approached significance for decreased birth weight among women consuming large quantities of caffeine. Used in moderation, caffeine consumption in pregnant women apparently does not pose a consistent, measurable risk to the human fetus with respect to congenital malformation, spontaneous abortion, or functional changes.