Epiphenomenon: 1. An additional symptom or condition that appears during the course of a disease. A doctor might ask if you have noticed any epiphenomena recently as a way of inquiring as to whether you have experienced additional symptoms or signs of illness.
2. Any occurrence that is accidental, accessory, or incidental to a cause-and-effect relationship. An increase in breast cancer risk with antibiotic usage may be an epiphenomenon if it is not the antibiotic, but the reason for the antibiotic use, namely inflammation, that is associated with breast cancer.