A 1995 study suggests that humans become tolerant to their daily dose of caffeine—whether a single soda or a serious espresso habit—somewhere between a week and 12 days.
They don't link the actual study or give any more detail on it. I suspect it might be pretty useless since the dose was apparently left to the user. But maybe the rest of world has missed this one important study...
In contrast, a recent review says:
Although complete tolerance does not occur at low doses, tolerance to some of the effects of caffeine can occur after chronic administration of very high doses of the drug (i.e., 750–1200 mg/day).
Juliano LM. Ferré S. Griffiths RR. Saitz R. The pharmacology of caffeine. In: Ries R.K., editor; Fiellin D.A., editor; Miller S.C., editor; Principles of Addiction Medicine. Fourth. Philadelphia, PA: Lippincott Williams & Wilkins; 2009. pp. 159–178.
I checked the latter book, which has something like 2 paragraphs on the topic, with about 8 citations, but none of the papers cited there is from 1995, nor does the book support the idea that any dose will cause tolerance (in fact it says almost exactly the same thing as the paragraph quoted above.)
So, my question is: can anyone locate the 1995 study Lifehacker mentions?