FYI, I found this (wiki):
The LD50 of caffeine in humans is dependent on weight and individual sensitivity and estimated to be about 150 to 200 milligrams per kilogram of body mass, roughly 80 to 100 cups of coffee for an average adult taken within a limited time frame that is dependent on half-life. Though achieving lethal dose with caffeine would be exceptionally difficult with regular coffee, there have been reported deaths from overdosing on caffeine pills, with serious symptoms of overdose requiring hospitalization occurring from as little as 2 grams of caffeine.[75][76][77][78] Death typically occurs due to ventricular fibrillation brought about by effects of caffeine on the cardiovascular system.
The 1/2 life is stated as 3-4 hours for an adult. Interestingly, this can be DOUBLED for women taking oral contraceptives (FYI Vash!) & can be 9 to 11 hours for pregnant women.
I suppose estrogen uses the same P450 system.
Anyway, sorry for the digress, but women, those thinking of getting pregnant, and those in health care will find this interesting, I think.