Coffee is the most widely consumed psychoactive substance on earth, and for most adults, it is safe and even beneficial in moderate amounts. But the line between optimal and excessive depends on individual genetics, body weight, medication interactions, and timing. The FDA provides general guidelines, but your personal limit may be higher or lower.
FDA Caffeine Guidelines
Healthy adults: 400 mg/day (about 4 cups of brewed coffee) Pregnant women: 200 mg/day (about 2 cups) Adolescents: 100 mg/day (about 1 cup) These are maximum limits, not targets. Many people do well with less.
Caffeine Content by Beverage
| Beverage | Serving | Caffeine |
|---|---|---|
| Drip coffee | 8 oz | 95–165 mg |
| Espresso | 1 shot | 63 mg |
| Cold brew | 12 oz | 150–240 mg |
| Black tea | 8 oz | 25–48 mg |
| Green tea | 8 oz | 25–35 mg |
| Energy drink | 16 oz | 150–300 mg |
| Cola | 12 oz | 34–46 mg |
Caffeine Half-Life and Timing
Caffeine has a half-life of 5–6 hours in most adults. This means 200 mg of caffeine at 2:00 PM still has 100 mg active at 7:00 PM and 50 mg at midnight. For good sleep hygiene, stop caffeine intake 8–10 hours before bedtime. Track your caffeine decay with the Coffee Calculator.
Signs of Too Much Caffeine
- Anxiety and jitters
- Insomnia (even when you feel tired)
- Digestive issues
- Rapid or irregular heartbeat
- Headaches (also a withdrawal symptom)
Key Takeaways
- 400 mg/day is the FDA safe maximum for healthy adults (about 4 cups).
- Caffeine half-life is 5–6 hours — stop 8–10 hours before bed.
- Cold brew and energy drinks pack significantly more caffeine than regular coffee.
- Genetics determine your sensitivity — some people metabolize caffeine 2–3x faster than others.
Frequently Asked Questions
Is coffee bad for you?
In moderate amounts (2-4 cups per day), coffee is associated with reduced risk of type 2 diabetes, Parkinson's disease, liver disease, and depression. Excessive amounts can cause anxiety, insomnia, and digestive issues. Individual response varies.
Can you build a tolerance to caffeine?
Yes. Regular caffeine consumption causes your body to produce more adenosine receptors, reducing the stimulant effect. Most tolerance develops within 1-2 weeks of daily use. A caffeine reset (1-2 weeks off) can restore sensitivity.
What is the best time to drink coffee?
Between 9:30-11:30 AM and 1:30-5:00 PM, when cortisol levels naturally dip. Avoid coffee within the first hour after waking (cortisol is already high) and after 2-3 PM if you are sensitive to sleep disruption.