Appendix 1. Search strategy for MEDLINE (via Ovid)

1. Acetaminophen/

2. (acetaminophen or paracetamol or Panadol or Tylenol).mp.

3. 1 or 2

4. exp Neoplasms/

5. (neoplasm* or malignan* or tumour* or tumor* or cancer* or carcinoma*).mp.

6. 4 or 5

7. exp Pain/

8. (pain* or nocicept* or neuropath*).mp.

9. 7 or 8

10. randomized controlled trial.pt.

11. controlled clinical trial.pt.

12. randomized.ab.

13. placebo.ab.

14. drug therapy.fs.

15. randomly.ab.

16. trial.ab.

17. 10 or 11 or 12 or 13 or 14 or 15 or 16

18. 3 and 6 and 9 and 17

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, Higgins 2011).

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

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

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

4. 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:

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

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

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

4. imprecision of results (wide confidence intervals);

5. high probability of publication bias.

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

1. large magnitude of effect;

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

3. dose‐response gradient.