What happens when someone drinks 30 cup of coffee per day?

You'll probably pee a lot. More seriously, the LD50 (mean lethal dose) of caffeine is probably about 130 mg/kg of body weight, though that number is derived from studies with some very jittery mice. read more

All that said, at 30 cups of coffee a day (that's 10X what many medical folks consider to be an optimal maximum) you will at least notice some of the many of the usual effects of excessive caffeine consumption that have been listed in detail in other Quora posts (some by me): insomnia, nervousness, restlessness, stomach irritation, nausea, increased urination, increased heart rate and respiration, to cite a few. read more

Parkinson's disease: Coffee is linked to a reduced risk of Parkinson's, with the greatest reduction seen at 5+ cups per day . Depression: Studies have shown that 4+ cups of coffee per day are linked to a 20% lower risk of depression and 53% lower risk of suicide (21, 22). read more