Read throught the forum and archives and read the thousands of testimonies and some of the detox symptoms that can occur.

Read the Detox stages in the FAQs to get an idea on the cleansing timeline.

The Master-Cleanse isn't really a fast, although people (including me) often refer to is that way. I think the only true "fast" is where you drink only water.

That said, if you do the Master-Cleanse as written, you will get enough calories so that you shouldn't faint. You will experience detox symptoms as Pepe pointed out, and those vary from person to person and even from cleanse to cleanse.

I've done six MC's without any real problems.