If you arent going to get your bllod work done, you are always taking a risk. You may have a liver proble you dont know about, and even a short 4 week run could fuck you up. Happened to a guy on the board i know personally. Assuming you are in good health, 6 weeks of winny should be a problem. If you want to run it longer that that, have your values checked at the six week mark and about 3 weeks after that. The test is cheap, dont be stupid and scimp out on the 50 bucks.