Concomitant therapy intake (i.e., drugs other than the study drug) could potentially be used as an outcome measure in therapeutic trials in musculoskeletal disorders. The objective of this Special Interest Group (Part 1) was to investigate this possibility. Concomitant therapy intake could be used as an outcome measure in 2 ways: either as an associated outcome measure if it was determined there was interaction between the study drug and the concomitant drug, or as an outcome measure in itself if concomitant drug intake was deemed important in its own right and fulfilled the OMERACT filter requirement. These 2 aspects were discussed in the session and then put to a vote.