**2. Method**

#### **2.1 Data sources and searches**

A review of the literature was carried out in Pubmed, Web of Science, Medline and PEDro databases. The search was limited to studies on adverse effects and possible complications due to invasive/needling techniques: acupuncture, injections and dry needling in English and Spanish.

The keywords in English first introduced separately were: "acupuncture", "injection", "dry needling" and "adverse effect/event". In a second time, in order to limit the article sample, 12 searches were added: 1–3: "acupuncture/dry needling/ injection" AND "complication"; 4–6: "acupuncture/dry needling/injection" AND "iatrogenic"; 7–9: "acupuncture/dry needling/injection" AND "safe practice" and 10–12: "acupuncture/dry needling/injection" AND "academic training". A manual search of the references of pre-selected articles was also carried out.

The search fields were title/abstract of the keywords of the studies publishes by the journals indexed in Pubmed during the period between 2000 (January) AND 2020 (January). In Web of Science the search fields were TS (theme)/TI (title). In Medline search field was TI (title) and in PEDro a simple search was done. The manuscripts selected for this systematic review met the following inclusion criteria: (i) articles that report the adverse effects and/or complications of invasive/needling techniques; (ii) reviews of such complications; (iii) articles in English and Spanish and (iv) articles with protocols or recommendations on the safe practice of these techniques. We excluded theoretical articles on the application of these techniques and articles that were not published in English or Spanish.

#### **2.2 Study selection and data extraction**

**Type of articles:** randomized clinical trials, case reports and reviews were included in this review. Letters to editor, commentaries to other articles and practical application of these techniques were excluded.

**Type of participants:** participants of all ages/nationalities/sex/gender/education level/socioeconomic status which has been treated with needling therapies.

**Type of interventions and outcomes:** articles which have reported adverse effects (mild-severe) due to acupuncture, dry needling and injection were selected.

**Type of publications:** full text articles published in English or Spanish. Once the articles were found, randomized clinical trials, case reports and reviews were selected. Once duplicates were removed, 2 reviewers analyzed the abstracts in a first screening and then carried out an exhaustive reading of the preselected ones until obtaining the final sample of articles reviewed and included in this study. If there was disagreement among the independent reviewers, a third reviewer decided. The data were extracted independently by the reviewers.

**Data extraction**: tables summarize the different adverse effects in chronological order classified in relation of the type of intervention.

**Quality assessment**: both authors selected, reviewed and assessed the quality of studies included in this review. Discrepancies were resolved by consensus.
