Up to 85 percent of women who are pregnant experience nausea, and nearly one half report vomiting. These symptoms (morning sickness) usually resolve by the end of the third month, but symptoms persist in an estimated 20 percent of pregnant women. Two percent report nausea and vomiting throughout pregnancy, and the condition is severe (hyperemesis gravidarum) in 0.3 to 3 percent of these women. Although many medications are available to relieve morning sickness, interventions are limited by concerns about adverse effects on the developing fetus. These concerns have led to interest in alternative remedies. Borrelli and colleagues reviewed the evidence regarding the safety and effectiveness of ginger, one of the most commonly used alternative preparations for morning sickness.

The authors conducted a systematic literature search to identify double-blind, randomized controlled trials (RCTs) that studied the effectiveness of ginger therapy. For safety issues, all clinical data were considered, including case reports. Manufacturers of products containing ginger provided published or unpublished data that could contribute to the review. Several reviewers independently assessed each study for quality using the Jadad scoring system. A formal meta-analysis was not possible because of the wide variation in design and outcomes used in the studies.

Of the 33 potential clinical trials, six RCTs used ginger alone (i.e., not combined with any other substance) to treat nausea and vomiting in early pregnancy. Five of the six RCTs received maximal Jadad scores. Outcome measures included Likert scales; symptom diaries; the Rhodes Index of Nausea, Vomiting, and Retching (an eight-item standardized tool); and the Medical Outcomes Study 36-Item Short Form Health Survey. Four studies compared ginger with placebo, and two used vitamin B₆ as the comparison agent. Four RCTs with a total of 237 mothers concluded that ginger was superior to placebo. Two additional RCTs with a total of 363 mothers concluded that ginger was as effective as vitamin B6.In the larger of these trials, symptoms and general health improved with both treatments, but 20 percent of mothers continued to use antiemetics after the study.

Safety was addressed in five RCTs and one prospective observational cohort study. No adverse effects were reported during ginger therapy, but belching was more common in patients taking ginger than those taking vitamin B6. No adverse effects (e.g., fetal loss, gestational age at delivery, congenital abnormalities, type of delivery) were recorded in women taking ginger compared with those taking vitamin B₆ and those taking placebo.

The authors conclude that ginger may be a safe and effective treatment for nausea and vomiting for morning sickness, but more studies are needed.