As always it depends. For instance the approved protocol may require evidence of certain medical history parameters or it might state that the interview with the subject was enough. It might also be good to think of this problem in advance and relate it to a risk based approach. So, for a marketed IMP, which is being used very similarly to the label and not involving innovative trial design or measures, there may be no need to verify the verbal history unless it was of vital safety importance.
The MHRA GCP Guide (2012) [See the RQA webcast on the MHRA Guide for details] :-
“subjects recruited via general advertisements and the investigator is not the primary care provider, past medical history will need to be obtained from the subject and the record of this may be the only source document available for the eligibility assessment. However, this could be subsequently verified by other means: for example, by the subject’s GP”. 11.5 Study documentation
However for Phase I it states:- "Ideally .., the unit should make every effort to verify their medical history ...... This could include for example, questioning the subject about their own and relevant family medical history and contacting the GP.... For FIH trials, part of the MHRA scheme, must have a robust and formalised procedure ...”12.12. 5 [N.B. “must” has no reference]
Also look at the RQA GCP Q & As. There is one on use of historic data and some on subject recruitment.
It would be interesting to hear from others.