Estrogen is stored in the body and can be held by fat or by converting it to estrone then back to estradiol. If you don't make a habit of it, you can go a few days and still have some estrogen in your system but it's best to keep constant levels in your system. If you have a spike in your blood stream, the half life is only a few hours but most delivery methods tend to avoid the spike. Sublingual tends to be the most common way of producing a spike and levels of estradiol could go from 1000 to 100 pg/ml over a 12 hour time period. Oral may not be the best deliver system but it produces pretty constant levels.
