A medicinal brew was a beverage with medicinal properties.
In 2370, Quark brought a "medicinal brew" to Julian Bashir and claimed it was a token of thanks from Bajoran monks, to show how much they appreciated his participation in their fundraiser for the Bajoran War Orphans Fund. It was supposedly an ancient secret of their order, and it was to impart great energy and vigor. Quark also said he was sure the drink was completely natural and that monks stated the whole thing should be drunk in one gulp to get the proper effect. Curious about its contents, Bashir performed a substance analysis report which revealed it to be an anesthetic containing water, sucrose, dextrose, tribnel root extract, grain particulates, yeast, synthehol, and 17 milligrams of hyvroxilated quint-ethyl metacetamin. According to Bashir, he'd hardly be able to stand, let alone play racquetball, if he drank it. (DS9: "Rivals")