I'm on 6MP since a bit over 5 months. I started with 75 mg and boy, was I miserable! I take 50 mg now since around 2 months and I feel great. I have blood tests once a month and they come back fine now (since I am on 50 mg). And I am in remission since 4 months.
I have to say that I love to hate 6MP. The side effects on 75 mg were terrible. I tried to sit them out. I constantly had bad headaches, dizzy spells, comatose sleep, achy body, nausea to the point of almost throwing up, sweating, total weakness (I couldn't even bend down to empty the dishwasher from the weakness in my legs). I am doing great now on 50 mg. I'm still more tired than before (meaning pre-6MP), but since I take it in the evening, it almost works like a sleep aid for me. I have at least 8 hours of uninterrupted sleep (except for tornado season and severe storms at nights - hey, I'm in Texas :)). My doc took me off 75 mg and put me on 50 mg after my blood work was borderline severe, meaning the blood count plummeted and the liver enzymes went through the roof. But I am doing okay now and I'm glad I didn't give up on 6MP.
I can only agree to what Sherry has said: Drink lots of fluids! To flush the kidneys and to keep you hydrated. My doc always says that 6MP makes you prone to dehydration, so chug down that water or whatever you like.
Just my 2 cents.