Ideally, you'll feel reinvigorated a few days into juice cleanse, but the first couple of days can be rough. "People usually feel a little funky at first," Haas says. "It usually takes three days to really start feeling good."
The reason is your body is screaming for all of the things it has grown accustomed to – like excess sugar, which Hyman says is eight times more addictive than cocaine, so withdrawals can be brutal. If you don't start feeling better by day three, Haas says you're probably dehydrated. Since you're peeing out so much fluid while cleansing, you really have to pound the water.