The psychological effect of a screening programme and clinical trial for hypertension upon the participants.

Two hundred and thirty-five entrants into the MRC trial for mild to moderate hypertension were matched with control subjects in order to assess the psychological effects of a screening programme and recruitment into a clinical trial. The prevalence and incidence of psychiatric morbidity among the trial participants were compared with those of the controls by means of responses to a self-administered questionnaire and diagnostic psychiatric interviews. No differences among the groups were shown between screening and entry into the trial, but after entry the prevalence of psychiatric morbidity among the trial participants fell. This was due to a greater improvement of those with psychiatric symptoms at entry in this group, the incidence of new morbidity being similar among the groups.