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The GRA in Shulchan Aruch Yoreh Deah 179:13 is pretty clear: the medicines in the Gemara really worked. I think that the fear in saying that to students stems from a general problem in Day School education today - a belief in science that is stronger than a belief in the Torah.
If I were teaching that sugya, I would bring in an article that
appeared in the NY Times Science supplement about a month ago. It appears that scientists found a mummified person that they date as having passed on some 5400 years ago (they called him "the Iceman") - which would make him a contemporary of Adam HaRishon. They found around his neck a fungus of local variety, which they originally thought was a good-luck charm. Upon performing an autopsy (now there's Kavod HaMet for you), they found that he was suffering from an intestinal parasite whose only cure, until discovery of the "new world" about 500 years ago, was that very fungus that he had around his neck.
Now, if people in the time of Adam HaRishon knew that much about medicine, why should we think less of Hazal?</HTML>