That morning cup of coffee or early afternoon soda is probably OK. But more than 500 to 600 milligrams of caffeine a day, or about four to seven cups of coffee, can cause restlessness, anxiety, headaches and other problems. Know how much caffeine is in your diet. You may be getting more than you think. To cut back, try one less can of soda or a smaller cup of coffee each day. Replace caffeinated drinks with decaf ones. Or brew tea for less time to reduce caffeine.