You bring up a good point. I am on day 2 and this is my first time doing the Master Cleanse. I have a kidney infection and am taking cranberry tablets which contain additional herbal supplements. So far, I've not suffered any ill side effects. I am not a purist either and am not going to kid myself about it.
I suggest you try Cascara Sagrada as a laxative. You can buy it in liquid form which is easier to regulate. Cascara Sagrada is a gentle laxative so it doesn't give you cramps when used it moderation and yet it's very effective. I would stick to the drops rather than the tablets.