Cramp bark is a plant that grows in North America. Historically, Native Americans used cramp bark as medicine for reducing swollen glands and treating fluid retention, mumps, and eye disorders. They also smoked cramp bark as a substitute for tobacco. These days, the bark and root bark of this plant are still used for healing. As the name suggests, cramp bark is used for relieving cramps, including muscle spasms, menstrual cramps, and cramps during pregnancy. Cramp bark is also used as a kidney stimulant for urinary conditions that involve pain or spasms.