Concomitant means at the same time.
In clincial trials, researchers often record information about concomitant conditions and concomitant therapy. A concomitant condition is a condition other than the one being studied. For example in a cystic fibrosis trial, an example of a concomitant condition is cancer, or heart disease. A concomitant medicine is a medicine taken by a clinical trial participant that is different to the medicine being studied.
Example: In a clinical trial of a CFTR modulator, if a participant takes paracetamol, researchers would record this as a concomitant medicine.