An acute overdose of caffeine, usually in excess of 250 milligrams (more than 2-3 cups of brewed coffee), can result in a state of central nervous system overstimulation called caffeine intoxication. The symptoms of caffeine intoxication may include restlessness, nervousness, excitement, insomnia, flushing of the face, increased urination, gastrointestinal disturbance, muscle twitching, a rambling flow of thought and speech, irregular or rapid heart beat, and psychomotor agitation.
In cases of extreme overdose, death can result. The median lethal dose (LD50) of caffeine is 192 milligrams per kilogram in rats. The LD50 of caffeine is dependent on weight and individual sensitivity and estimated to be about 150 to 200 milligrams per kilogram of body mass, roughly 140 to 180 cups of coffee for an average adult taken within a limited timeframe that is dependent on half-life. Though achieving lethal dose with coffee would be exceptionally difficult with regular coffee, there have been reported deaths from intentional overdosing on caffeine pills.
Treatment of severe caffeine intoxication is generally supportive, providing treatment of the immediate symptoms, but if the patient has very high serum levels of caffeine then peritoneal dialysis, hemodialysis, or hemofiltration may be required.