According to the Department of Agriculture's latest Dietary Guidelines for Americans, up to 400 mg of caffeine per day—the amount in two to four 8-ounce cups of coffee—can be part of a healthy diet for adults. The Food and Drug Administration says 600 mg per day is too much.11-Sept-2016
Regular use of more than 600 mg of caffeine might cause the short-term effects listed above. Long-term effects at this level may include chronic insomnia, constant anxiety, depression, and stomach problems. It can also cause high blood pressure or make high blood pressure worse.
It reaches a peak level in your blood within 30 to 60 minutes. It has a half-life of 3 to 5 hours. The half-life is the time it takes for your body to eliminate half of the drug. The remaining caffeine can stay in your body for a long time.
Up to 400 milligrams (mg) of caffeine a day appears to be safe for most healthy adults. That's roughly the amount of caffeine in four cups of brewed coffee, 10 cans of cola or two "energy shot" drinks.
Studies show that 100 to 200 mg of caffeine (about 1 to 2 cups of regular coffee) are enough to achieve these results. When caffeine consumption climbs to 250 to 700 mg per day, people may experience nausea, headaches, sleep difficulties or increased anxiety. People may have heart palpitations with more than 1,000 mg.
How Much is Too Much Caffeine? In humans, more than 150-200mg per kg of body weight, or 5 to 10 grams of total caffeine ingested is considered lethal.
Studies show that 100 to 200 mg of caffeine (about 1 to 2 cups of regular coffee) are enough to achieve these results. When caffeine consumption climbs to 250 to 700 mg per day, people may experience nausea, headaches, sleep difficulties or increased anxiety. People may have heart palpitations with more than 1,000 mg.
summary. A caffeine crash can result due to poor sleep, consuming caffeine close to bedtime, or consuming too much. It's associated with tiredness, the inability to concentrate, and irritability.