Here's a bit of advice about caffine for anybody considering the Master Cleanse.

If you drink more than one caffinated beveridge a day, do not go cold turkey on the Master Cleanse.

Caffine is a vasoconstrictor. This means it makes your blood vessles constrict (become smaller). Caffine is also a long acting drug.

If you quit caffine very suddenly, after about 12 hours WHAM!!! your blood vessels dialate. In your head, this means they start pressing on several nerves and cause you intense pain. As a migrane sufferer, I can tell you it's the next best thing to a migrane. (In fact, the pain of a migrane is caused by sudden vasodialation. Caffine withdrawl is different from a migrane only in that you lack the nausea, sensitivity to light and noise, and/or screwed up vision and hearing on top of all that pain.)

Spare yourself migrane level pain. Step yourself down off of caffinated drinks before starting your MC. It won't be easy. It won't be fun. You'll yawn so much you think your jaw is going to fall off. But it beats the hell out of an all day, oh my god I didn't know they made pain like this headache.