The gris-gris is typically used to sort out matters in love, finance, luck, legal issues or to reverse a hex. Once the voodoo practice was brought to America and integrated into slave culture, the meaning changed from mostly positive intentions to negative. Slaves used it as a spiritual method to bring evil spirits to their slave owners. Some of the gris-gris bags were placed on the gravestones of slave owners.
In Louisiana, where the practice of voodoo is well-known, the gris-gris is used as a symbol of black magic. It includes two types of magic, homeopathic and sympathetic. Sympathetic is a symbol made to look just like the person intended. Homeopathic uses hair, clothing or something attached to the subject.
More information about the use of the gris-gris can be found at the New Orleans Historic Voodoo Museum in New Orleans, Louisiana.