From eJahan Official Wiki

Juice can immediately increase health.

• You can drink juice from profile page (My Places - Profile), picture "drink juice".
• If you have in your inventory juices of varying quality in the first place the juice of higher quality will be used.
• By drinking juice health restores as much as it has stars.
• There is a limit, from day 209 you can drink only 20 glasses of juice (players confirms that only 10 glasses can be drunk), and thus not recover more than 50 units of health.
• Two points of productivity produces one juice.