There’s a very old-fashioned, very famous Italian liqueur made of… rhubarb. (Well, actually Chinese rhubarb, which has an earthier taste. So it kinda tastes like Chinese medicine, apparently.)
Rabarbaro Zucca Amaro Liqueur was created in 1845. King Victor Emanuele liked it in cocktails as a sort of bitters (“amaro”). Besides rhubarb root, it includes cardamom seeds, China fruit, bitter orange peel and other secret herb ingredients. 16% alcohol.
The funny thing is that I really like the taste of most of these “medicinal” liqueurs and liquors, because I like a lot of herbs. OTOH, I really hate a lot of the stuff other people like (ie, those disgusting shots/cocktails that a lot of people are into). So I would probably like this rhubarb thing, especially since I have a mad passion for cardamom. The bitter-orange rind is the only thing that sounds a bit nasty.
What I don’t like much is any kind of quinine flavor, as in tonic water. Maybe now that I’m older I’ll like it more, and it is healthy for you. But bleh!