A review of the scientific literature found that ginger (Zingiber officinale) prevented nausea due to pregnancy, seasickness, chemotherapy and surgery in five out of six placebo studies. The dose used in these studies was 1 g of fresh or powdered ginger. In another study at Thailand’s Chiang Mai University, thirty-two women who took ginger in the first half of their pregnancy had about half the nausea and vomiting from morning sickness as pregnant women taking placebo capsules. The women took four capsules of ginger (250 mg each) four times a day. In some cases, it took a couple of days for the herb to take effect. This backs up a Danish study in which ginger relieved nausea in pregnant women, most of whom had to be hospitalized because their nausea was so severe. Ginger’s active compounds, called gingerols, are thought to act on the central nervous system and/or to increase movement in the digestive system. Although the German Commission E monographs warn that pregnant women should not take ginger because two 1980 Japanese studies showed that isolated compounds may cause cell mutations, no adverse effects were reported in the Japanese studies and there is no evidence that ginger itself harms mother or baby.
Sources: Ernst, E., and M. H. Pittler. “Efficacy of ginger for nausea and vomiting: A systematic review of randomized clinical trials.” British Journal of Anaesthesia 2000, 84(3): 367–371.