Common side effects of caffeine can include disruption to sleep patterns; restlessness and anxiety; and stomach irritation, including nausea and vomiting. Elevated heart rate in healthy adults may also occur when consumed in moderate to high amounts, according to WebMD.
Adults suffering from certain conditions, disorders and illnesses are at risk for additional side effects from caffeine consumption. WebMD states that caffeine consumption can worsen certain mental illnesses, such as anxiety and bipolar disorders, as well as conditions concerning the circulatory and cardiovascular systems, such as high blood pressure, heart disease, bleeding disorders and diabetes. In addition, individuals who experience diarrhea, epilepsy, glaucoma, irritable bowel syndrome and osteoporosis may also experience heightened symptoms of their pre-existing conditions.
Caffeine consumption by children when limited to levels commonly found in food and beverages is likely to be safe with few side effects. However, women who are pregnant or breastfeeding are advised to limit or discontinue their use of caffeine as it may adversely affect infants. WebMD links caffeine usage to increased risk of miscarriage in pregnant women and irritability, sleeplessness and increased bowel movements in breastfeeding infants. While caffeine in moderate doses has minimal sides effects, WebMD warns that when consumed in very high doses caffeine can cause irregular heartbeats and even lead to death.