1. Characteristics of excluded reviews.

Study	Reason for exclusion
Alviar 2011	Opioids studied but not at high doses specifically
Bao 2016	Cancer pain
Bell 2012	Cancer pain
Brettschneider 2013	No opioids studied
Cepeda 2006	Opioids studied but not at high doses specifically
Chaparro 2012	Opioids studied but not at high doses specifically
Chaparro 2013	Opioids studied but not at high doses specifically
Cheong 2014	No opioids studied
de Oliveira 2016	Opioids studied but not at high doses specifically
Duehmke 2006	Opioids studied but not at high doses specifically
Enthoven 2016	Opioids studied but not at high doses specifically
Fraquelli 2016	Acute pain
Gaskell 2014	Opioids studied but not at high doses specifically
Gaskell 2016	Review with no included studies
Hadley 2013	Cancer pain
Hróbjartsson 2010	No opioids studied
Marks 2011	No opioids studied
McNicol 2013	Opioids studied but not at high doses specifically
McNicol 2015	Withdrawn from publication
Moore 2015a	No opioids studied
Mujakperuo 2010	No opioids studied
Nicholson 2017	Cancer pain
Quigley 2013	Withdrawn from publication
Radner 2012	No opioids studied
Ramiro 2011	Opioids studied but not at high doses specifically
Richards 2011	Opioids studied but not at high doses specifically
Santos 2015	Opioids studied but not at high doses specifically
Schmidt‐Hansen 2015a	Cancer pain
Schmidt‐Hansen 2015b	Cancer pain
Seidel 2013	Opioids studied but not at high doses specifically
Singh 2015	No opioids studied
Staal 2008	Opioids studied but not at high doses specifically
Stannard 2016	Opioids studied but not at high doses specifically
Stanton 2013	No opioids studied
Straube 2014	Cancer pain
Whittle 2011	Opioids studied but not at high doses specifically
Wiffen 2015a	Opioids studied but with mixed cancer and non‐cancer group
Wiffen 2015b	Cancer pain
Wiffen 2016	Cancer pain
Zeppetella 2015	Cancer pain