Cramp bark is a colloquial name for shrubs identified by the scientific name of Viburnum opulus. It is also known by a number of other common names, including Dog Rowan Tree, King's Crown, May Rose, Black Haw and Cranberry Tree. This shrub, which is native to the British Isles, and has been introduced into some parts of America and Canada, can grow quite large, sometimes up to 16 feet (five meters) tall and 16 feet (five meters) in width.
This shrub is a member of the family of plants called Caprifoliaceae, which includes honeysuckle shrubs, and like some species of honeysuckle it bears white flowers that can grow up to five inches (about 13 cm) in size. The flowers give rise to red berries that are edible if cooked. These berries contain large quantities of vitamin C, and are sometimes eaten in a similar way to cranberries.
Cramp bark tea has long been used to treat uterine cramps, or period pains. It contains a substance called scopoletin, which is a kind of muscle relaxant that tends to ease spasmodic muscle contractions. Cramp bark tincture has also been used to treat the premature onset of labor in pregnant women, when it may be successful in stopping uterine contractions that have commenced too early. Cramp bark herb extracts are sometimes marketed to pregnant women as an aid that may help to strengthen the uterine muscles in preparation for labor. As with any herbal supplements, pregnant women are usually advised to check with their physician prior to taking any supplement of this nature.
Cramp bark extract is usually prepared by stripping bark from the roots of the shrub rather than from the branches. The bark thus obtained may then be dried and powdered. Alternatively, the bark may be soaked in a fluid such as alcohol or another solute, to obtain a tincture containing the active substance.
Other cramp bark benefits may include relieving muscular pain such as cramps in the leg or neck, and lowering blood pressure. The effect on blood pressure is believed to be due to the relaxation of the muscular walls of the blood vessels. Cramp bark side effects may include stomach problems such as nausea, diarrhea, and vomiting. Skin rashes may also be experienced. Side effects are usually only seen if the cramp bark extract is taken in high dosages, however, and at low dosages many people report no adverse side effects.