Caffeine stimulates the central nervous system. An overdose can trigger an anxiety panic attack in some people. An overdose greater than 10 g of caffeine can be fatal in adults. However, a daily intake of around 400 mg—about four or five cups of coffee—is considered safe for most adults.
Some people’s genes make them more sensitive to caffeine. Children, pregnant women, people with a history of insomnia, restlessness, anxiety, tremors, panic attacks, irregular heartbeat, heart attack, or high blood pressure should avoid or abstain from caffeine consumption in coffee and other products.