A Cochrane review included 41 trials involving a total of 5 449 women. Ginger, vitamin B6, and several antiemetic drugs were studied. There was a trend favouring ginger compared to placebo, but the results were nonsignificant and not consistent. There was no difference in nausea in studies comparing ginger with vitamin B6. In 2 trials comparing vitamin B6 with placebo the reduction in nausea score was nonsignificant (RR 0.92, 95% CI 0.40 to 1.44; n=393 ). The evidence about anti-emetic drugs was very limited. Information on maternal and fetal adverse outcomes was sparce.
Another Cochrane review included 25 trials involving a total of 2 052 women, but the majority of 18 different comparisons included data from single studies with small numbers of participants. In a study with 92 participants, women taking vitamin B6 had a slightly longer hospital stay compared with placebo (mean difference (MD) 0.80 days, 95% CI 0.08 to 1.52). There was insufficient evidence to demonstrate a difference in other outcomes including mean number of episodes of emesis (MD 0.50, 95% CI -0.40 to 1.40) or side effects.
Comment: The quality of evidence is downgraded by shortcomings in study quality, by indirectness (differences in studied patients), and by inconsistency (heterogeneity in interventions and outcomes).