For most healthy adults, consuming up to 400 milligrams (mg) of caffeine per day is considered safe. This amount is roughly equivalent to four cups of brewed coffee or about 10 cans of cola

. However, consuming 400 mg of caffeine all at once is not recommended; single doses should ideally be limited to about 200 mg to avoid adverse effects such as increased heart rate, anxiety, jitteriness, and sleep disturbances

. Exceeding 400 mg daily or consuming very high single doses can lead to caffeine overdose, which may cause symptoms ranging from dizziness, headache, and insomnia to more severe effects like irregular heartbeat, confusion, hallucinations, and convulsions

. Caffeinism, a state of caffeine overdose, typically occurs at daily intakes of 1 to 1.5 grams (1000–1500 mg) or more, with symptoms including nervousness, irritability, restlessness, and palpitations

. Special populations such as pregnant or breastfeeding women are advised to limit caffeine intake to less than 200 mg per day

. Children and adolescents should also avoid excessive caffeine consumption due to increased sensitivity and potential health risks

. In summary:

• Safe daily limit for most healthy adults: Up to 400 mg/day
• Recommended maximum single dose: About 200 mg
• Pregnant/breastfeeding women: Less than 200 mg/day
• Risk of overdose symptoms: Above 400 mg/day, especially with large single doses
• Severe overdose (caffeinism): Around 1000 mg or more per day

If you experience symptoms like rapid heartbeat, severe anxiety, or confusion after caffeine intake, seek medical advice promptly