%J BMJ %A Brennan C Kahan %A Edmund Juszczak %A Elaine Beller %A Megan Birchenall %A An-Wen Chan %A Sophie Hall %A Paul Little %A John Fletcher %A Robert M Golub %A Beatriz Goulao %A Sally Hopewell %A Nazrul Islam %A Merrick Zwarenstein %A Diana Elbourne %A Alan Montgomery %T Guidance for protocol content and reporting of factorial randomised trials: explanation and elaboration of the CONSORT 2010 and SPIRIT 2013 extensions %I BMJ %L discovery10204508 %C England %V 388 %O © The Author 2025. This is an Open Access article distributed in accordance with the terms of the Creative Commons Attribution (CC BY 4.0) license (http://creativecommons.org/licenses/by/4.0/). %D 2025