A frequent feature of pharmaceutical research is the open label extension study, in which patients participating
in double blind placebo controlled trials of new medications are invited, on completion of the
initial trial, to take the study drug for some further period. Patients are openly given the active substance
at this stage, regardless of their assignment in the initial trial. Investigators are typically reluctant to
unblind the patients’ assignment at the point of entry into the open label phase, on the grounds that this
may introduce ascertainment bias in the main study.
It is argued that patients invited to participate in open label extension studies cannot give a proper consent
to such research unless they know to which arm of the main trial they were recruited. It is further
argued that to recruit certain groups of patients from placebo controlled trials into open label extension
studies may also be unethical for clinical reasons
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