They are going to affect everyone a little differently, but a little of both. The pumps are retardedly strong. The hit your liver will take compared to the amount of muscle you'll put on, and keep on, are again, negligible. BP raise isn't worth it. The amount of shut-down isn't really worth it. I'd just stick to 3 weeks. You'll gain virtually the same amount as a 4 weeker and have less sides. Win Win.