I saw the following text in a job description for a pharmaceutical company:
"Issue blind breakers and dose assignment envelopes for blinded
studies that are not run by an Interactive Voice Response System."

What are "blind breakers"?

In the pharmaceutical industry, "breaking the blind" refers to the
process of revealing the name of the specific drug (or placebo, as the
case may be) that has been given to a participant in a double-blind
study or clinical trial. I have not encountered the term "blind
breaker," but I would guess that it may have to do with the paperwork
that is associated with breaking the blind in a drug trial.

http://www.childrens-mercy.org/stats/weblog2004/blind.asp

I found the term once in this context.  The site talked about
double-blind studies and the difficulties assuring that they were
unimpeachable.  From the quotation in the question:
"Issue blind breakers and dose assignment envelopes for blinded studies",
I could imagine that when the "dose assignment envelopes" are prepared
for distribution to the MDs in the study, there must also be prepared
a control record of what is actually in the envelopes (test drug &
dosage or placebo). This list could serve as a "blind breaker", but if
the drug being tested suddenly gave rise to serious side-effects, it
would be tedious and time-consuming to go back to this  record.
SO, I expect that along with the "dose assignment envelopes" the MDs
are also given a sealed envelope with the true info (maybe like PINs
are sent), so that when the alarm on side-effects goes off, each
doctor can immediately use this "blind breaker" to know if his patient
has been taking the drug and also could be subject to the side effect.

I hope it is that, that the studies anticipate this scenario.
Of course, at the end of the study, the sealed envelopes must be
returned with each MDs' findings to prove that the double-blind was
upheld.

Thank you both. Given the context, I'm now fairly certain that the
blind breaker must be the paperwork showing which patients recieved
the placebo and which ones are recieving the treatment.