On my old job, I could get these for free. I drank them that whole day, like 20+ cans. Then I took 2 weeks of holiday. I did not drink any caffeine during that time. Then I came back from my holiday, and I wasn't really thinking about it. So my first day back on the job, I again drank about 20 cans. WOW!!!! My heart was pounding for hours!!!!