Coffee and Caffeine FAQ

If this is true, it's probably because only a small percentage of the caffeine we ingest makes it into our bloodstream, as well as the fact that it takes time for it to absorb rather than getting into our blood all at once. Injecting 500 mg directly into the blood is, I guess, like drinking 50 cups of coffee in one second.

On an interesting side note, lung tissue is very poor at absorbing nicotine compared to the stomach and intestines. Smoking two cigarettes won't kill you, but eating two cigarettes would result in a fatal nicotine overdose. However, certain other substances are absorbed much better through the lungs than the stomach and intestines.