Sex: A change in our guidelines to authors to ensure that this is no longer an ignored experimental variable

Summary • BJP now requires sex to be considered as an experimental variable for all experimental reporting. This will affect the details of the experimental design that are documented or, in the absence of a design incorporating both sexes, a full justification for that approach. • We recommend that all experiments (in vitro, in vivo, and ex vivo) should include both sexes, unless there is a specific justification or exemption, such as when using immortalised cell lines or tissue derived from a sex organ. • Multifactorial designs should be used to study the overall effects of Sex, Treatment (i.e., the experimental intervention), and their interaction. • Authors should consider the implications for the study findings when testing males and females in close proximity, particularly in behavioural studies, and describe these implications in the discus- sion of the manuscript.