a person who does not reply to a communication such as a survey or questionnaire

a follow-up letter was sent to non-responders three weeks after the initial mailing

a person who does not respond, or does not respond satisfactorily, to a drug, therapy, or other treatment

non-responders are likely to respond if switched to an antidepressant with a different mechanism of action

if a patient is a non-responder after 12 weeks, there may be other causal factors (i.e. non-compliance)