Joints are made (rolled) by combining a Hempleaf and a Leaf. When consumed (smoked) the player is affected by the "fuddled" debuff with a huge amount of motion blur and vibrating colors on the screen. It wears off after some time (sleeping helps) and also can be cured by eating Bitterroot to induce vomit.
The joint heals 25 hunger and 25 thirst. Due to this and because hemp grows in just 2 game-days, one can use them as their only "food" item with no penalty other than the "fuddled" debuff.