The objective of this overview is to summarize existing knowledge about the effects of acupuncture-point stimulation on nausea and vomiting. Systematic reviews on postoperative nausea and vomiting, chemotherapy-induced nausea and vomiting, and pregnancy-related nausea and vomiting exist. Several randomised trials, but no reviews, exist for motion sickness. For postoperative nausea and vomiting, results from 26 trials showed acupuncture-point stimulation was effective for both nausea and vomiting. For chemotherapy-induced nausea and vomiting, results of 11 trials differed according to modality with acupressure appearing effective for first-day nausea, electroacupuncture appearing effective for first-day vomiting, and noninvasive electrostimulation appearing no more effective than placebo for any outcome. For pregnancy-related nausea and vomiting, results were mixed. Experimental studies showed effects of P6-stimulation on gastric myoelectrical activity, vagal modulation and cerebellar vestibular activities in functional magnetic resonance imaging. There is good clinical evidence from more than 40 randomised controlled trials that acupuncture has some effect in preventing or attenuating nausea and vomiting. A growing number of experimental studies suggest mechanisms of action.

The effects of acupuncture on health are generally hard to assess. Stimulation of the P6 acupuncture point is used to obtain an antiemetic effect and this provides an excellent model to study the efficacy of acupuncture. Thirty-three controlled trials have been published worldwide in which the P6 acupuncture point was stimulated for treatment of nausea and/or vomiting associated with chemotherapy, pregnancy, or surgery. P6 acupuncture was equal or inferior to control in all four trials in which it was administered under anaesthesia; in 27 of the remaining 29 trials acupuncture was statistically superior. A second analysis was restricted to 12 high-quality randomized placebo-controlled trials in which P6 acupuncture point stimulation was not administered under anaesthesia. Eleven of these trials, involving nearly 2000 patients, showed an effect of P6. The reviewed papers showed consistent results across different investigators, different groups of patients, and different forms of acupuncture point stimulation. Except when administered under anaesthesia, P6 acupuncture point stimulation seems to be an effective antiemetic technique. Researchers are faced with a choice between deciding that acupuncture does have specific effects, and changing from 'Does acupuncture work?' to a set of more practical questions; or deciding that the evidence on P6 antiemesis does not provide sufficient proof, and specifying what would constitute acceptable evidence.