For most healthy adults, consuming up to 400 milligrams of caffeine per day is generally considered safe and not associated with negative effects. This amount is roughly equivalent to two to three 12-ounce cups of coffee or about four cups of brewed coffee

. However, individual sensitivity to caffeine varies widely, influenced by factors such as genetics, health conditions, medications, pregnancy, and breastfeeding status. For example, pregnant or breastfeeding women are advised to limit caffeine intake to less than 200 milligrams per day

. Children and adolescents should consume much less caffeine, with recommendations around 3 mg per kilogram of body weight per day, as higher amounts can increase anxiety and other side effects

. Consuming extremely high doses of caffeine—around 1,200 milligrams rapidly or multigram doses on the order of 10 grams—can be toxic and even fatal, causing seizures and other serious health issues

. Pure or highly concentrated caffeine products pose significant risks and should be used with caution. Signs of too much caffeine intake include nausea, anxiety, irritability, headaches, nervousness, jitteriness, and heart palpitations (premature ventricular contractions)

. If caffeine consumption is stopped suddenly after high use, withdrawal symptoms may occur, so gradual reduction is recommended

. In summary:

• Safe daily limit for most adults: up to 400 mg caffeine (~2-4 cups of coffee)
• Pregnant/breastfeeding women: limit to 200 mg/day
• Children/adolescents: much lower, about 3 mg/kg body weight/day
• Toxic doses: 1,200 mg rapidly or more can cause serious harm
• Symptoms of excess: anxiety, nausea, irritability, heart palpitations

Adjust caffeine intake based on personal tolerance and health status, and consult a healthcare provider if uncertain