If you are poisoned in Don't Starve, you can either wait three days for the poison to run its course, or you can offer treasure to Wishing Wells found in Ancient Pig Ruins for a chance to be cured of the poison. Alternatively, you could drink Magic Water obtained from the Fountain of Youth. However, interacting with the fountain will spawn the Pugalisk. The easiest way I find using Anti Venom purchased from the Curly Tails Mud Spa found in Swinesbury.