That's not how human medical research works though. Single-blinded studies blind the patient. Double-blinded studies blind the patient as well as the researcher

That's not how human medical research works though. Single-blinded studies blind the patient. Double-blinded studies blind the patient as well as the researcher applying the treatment. If you make a trial for a new migraine pill, you want to know whether it actually works or whether the mere act of taking something and believing in it is what works. So you give half the patients the medicine and half the patients just sugar. They can't tell, so the mere act of taking a pill won't make a difference. If you also can't tell (double blind) then they can't (not even subconsciously) deduce from your actions whether they just the control group. If you would not give the control group a sugar pill, they could be stressed out about not getting treatment and just that fact would distort your result. For the most part, animal research works similarly, btw.