Appendix 1. Search strategy for Cochrane Database of Systematic Reviews (the Cochrane Library)

1. MESH descriptor Anti‐Inflammatory Agents, Non‐Steroidal OR (non‐steroidal anti‐inflammatory):ti,ab,kw

2. MESH descriptor Capsaicin OR capsaicin:ti,ab,kw

3. MESH descriptor Lidocaine OR lidocaine:ti,ab,kw

4. Rubefacient:ti,ab,kw

5. OR 1/4

6. MESH descriptor Administration, Topical OR topical:ti,ab,kw

7. 5 AND 6

Appendix 2. GRADE: criteria for assigning grade of evidence

The GRADE system uses the following criteria for assigning a quality level to a body of evidence (Chapter 12, Schünemann 2011).

• High: randomised trials; or double‐upgraded observational studies.

• Moderate: downgraded randomised trials; or upgraded observational studies.

• Low: double‐downgraded randomised trials; or observational studies.

• Very low: triple‐downgraded randomised trials; or downgraded observational studies; or case series/case reports.

Factors that may decrease the quality level of a body of evidence are:

• limitations in the design and implementation of available studies suggesting high likelihood of bias;

• indirectness of evidence (indirect population, intervention, control, outcomes);

• unexplained heterogeneity or inconsistency of results (including problems with subgroup analyses);

• imprecision of results (wide confidence intervals);

• high probability of publication bias.

Factors that may increase the quality level of a body of evidence are:

• large magnitude of effect;

• all plausible confounding would reduce a demonstrated effect or suggest a spurious effect when results show no effect;

• dose‐response gradient.