CathInfo.com

Probably like most other substances used as medication, dosage is the key. Too little has no effect leading to complaints of, “It doesn’t work.”
Of greater concern is the use of too much. A college roommate tried to write a paper for a class the evening before it was due next morning. She worked a 12 hour shift in a nursing home, ate a quick dinner, brewed up super strong coffee and got to work, drinking the joe, black with a ton of sugar and popping No-Doz tablets. Long story short, she ended up with bloody projectile vomit, chest pain, and heart palpitations. We called the ambulance and they pumped her stomach, started cleaning her out with IV liquids, something to calm her heart, potassium, and I don’t know what all. They kept her two nights hooked up to various monitors. To make matters worse, she was malnourished before the incident, anemic, low calcium, low potassium, deficient cholesterol, vitamins C, D, E, B-12, etc. That was because in the effort to stay slim, maintain her energy, and not take time to cook, she subsisted on a six-pack of Diet Pepsi, black coffee, and a Snickers bar per day. 
Oh, and she had an ulcer. No surprise.
She was ordered to take the rest of the semester off and eat a special diet and get sufficient sleep. She went home to her mother for the summer. Because the hospital and medical bills were so steep, she didn’t return in the Fall, opting instead for community college. 
Remember, MODERATION!