Abstract: We included 32 studies that involved a total of 2601 participants. Acupuncture was either manually stimulated (24 studies) or electrically stimulated (8 studies). The aetiology of gastroparesis was diabetes (31 studies) or surgery (1 study). All studies provided data on the proportion of people with symptoms 'improved', although the definition or categorisation of improvement varied among the studies. Most measured only short-term outcomes (28 studies), and only one study employed validated instruments to assess subjective changes in symptoms or reported data on quality of life or the use of medication. Reporting of harm was incomplete; minor adverse events were reported in only seven trials. Most studies had unclear risk of bias in terms of allocation concealment (29/32), outcome assessor blinding (31/32) and selective reporting (31/32), as well as high risk of bias in terms of participant/personnel blinding (31/32). Acupuncture was compared with sham acupuncture (needling on non-acupuncture points), three different types of gastrokinetic drugs (domperidone, mosapride, cisapride), and a histamine H₂ receptor antagonist (cimetidine). There was low-certainty evidence that symptom scores of participants receiving acupuncture did not differ from those of participants receiving sham acupuncture at three months when measured by a validated scale. There was very low-certainty evidence that a greater proportion of participants receiving acupuncture had 'improved' symptoms in the short term compared to participants who received gastrokinetic medication (4 to 12 weeks) (12 studies; 963 participants; risk ratio (RR) 1.25; 95% confidence interval (CI) 1.17 to 1.33, I² = 8%). Short-term improvement in overall symptom scores favouring acupuncture was also reported in five studies with considerable heterogeneity. Acupuncture in combination with other treatments, including gastrokinetics, non-gastrokinetics and routine care, was compared with the same treatment alone. There was very low-certainty evidence in favour of acupuncture for the proportion of participants with 'improved' symptoms in the short term (4 to 12 weeks) (17 studies; 1404 participants; RR 1.22; 95% CI 1.16 to 1.28; I² = 0%). Short-term improvement in overall symptom scores, favouring acupuncture, were also reported (two studies, 132 participants; MD -1.96, 95% CI -2.42 to -1.50; I² = 0%). Seven studies described adverse events, including minor bleeding and hematoma, dizziness, xerostomia, loose stool, diarrhoea, abdominal pain, skin rash and fatigue. The rest of the trials did not report whether adverse events occurred. Subgroup analyses revealed that short-term benefits in terms of the proportion of people with 'improved' symptoms did not differ according to the type of acupuncture stimulation (i.e. manual or electrical). The sensitivity analysis revealed that use of a valid method of random sequence generation, and the use of objective measurements of gastric emptying, did not alter the overall effect estimate in terms of the proportion of people with 'improved' symptoms. The asymmetric funnel plot suggests small study effects and publication bias towards positive reporting. There is very low-certainty evidence for a short-term benefit with acupuncture alone or acupuncture combined with gastrokinetic drugs compared with the drug alone, in terms of the proportion of people who experienced improvement in diabetic gastroparesis. There is evidence of publication bias and a positive bias of small study effects. The reported benefits should be interpreted with great caution because of the unclear overall risk of bias, unvalidated measurements of change in subjective symptoms, publication bias and small study reporting bias, and lack of data on long-term outcomes; the effects reported in this review may therefore differ significantly from the true effect. One sham-controlled trial provided low-certainty evidence of no difference between real and sham acupuncture in terms of short-term symptom improvement in diabetic gastroparesis, when measured by a validated scale. No studies reported changes in quality of life or the use of medication. Due to the absence of data, no conclusion can be made regarding effects of acupuncture on gastroparesis of other aetiologies. Reports of harm have remained largely incomplete, precluding assessments of the safety of acupuncture in this population. Future research should focus on reducing the sources of bias in the trial design as well as transparent reporting. Harms of interventions should be explicitly reported.

Plain-language summary: We analysed 32 studies that involved a total of 2601 participants. Most trials involved people with diabetic gastroparesis, who received short-term treatment (often four weeks). Non-profit funding bodies (the Chinese government and a university) funded six out of the 32 studies and the others did not report the funding source. One study compared real acupuncture with sham acupuncture (needling on non-acupuncture points). Twenty-eight trials compared acupuncture to a drug, or acupuncture with a drug or to the drug alone. A small number of trials compared acupuncture plus a non-drug treatment to the same treatment alone. The drugs in the trials were mostly gastrokinetic agents (such as domperidone, mosapride, and cisapride), which promote stomach emptying. Despite there being a small reported effect, we are uncertain about any benefit of acupuncture for symptomatic gastroparesis in the short term, when used alone or added to other treatments for gastroparesis (gastrokinetics, other medicines, or 'routine care'), due to the evidence being of very low certainty. There is no information to help understand any long-term benefits of acupuncture. The effects of acupuncture on symptoms of gastroparesis are probably little different from those of sham acupuncture in the short term. It is unclear whether acupuncture helps in gastroparesis after surgery or when the cause of gastroparesis is unknown, because there is not enough information. No trial studied the effects of acupuncture on quality of life or delayed emptying of the stomach. We do not know whether acupuncture is safe for people with diabetes who have delayed emptying of the stomach, because safety was incompletely reported in most trials. Overall, the certainty of evidence is very low. Most studies had design issues. We suspected the existence of unpublished studies and it was not possible to be sure whether those we identified fully reported their findings. There was no consistent definition of improvement across studies. Any reported benefit may not be accurate and should be interpreted with caution. Future trials should focus on valid measures of treatment effects reported directly by patients, and assessment of stomach emptying. Trials should meet quality standards for design and transparent reporting. The evidence is current to March 2018.