“Absinthe makes the heart grow founder” is a quote sometimes attributed to author/renaissance woman Ethel Watts Mumford. Although I distinctly remember Groucho Marx saying it at some point. Possibly to a small child.
At any rate, the extremely potent spirit (90 to 148 proof, according to Wikipedia) was banned in the U.S. in 1912 — well before Prohibition. That didn’t stop people from drinking it, of course. And any self respecting bartender had his own recipe for making it. Here is Caulkins’ version, from the Mixing Master manuscript.

Notes:
Caulkins’ has substituted juniper berries and angelica root for the traditionally used anise and fennel. The 11 U.P. refers to spirit of wine that is “11 under proof”. In other words, 11 parts water and 89 parts proof spirit (100 proof). Powerful stuff, indeed.
The Mixing Master has several recipes that include Absinthe. There is the traditional Absinthe Drip (future post spoiler alert!), which dilutes the spirit enough so that you won’t immediately and permanently destroy your brain cells. But interestingly, there are other recipes that call for a full Jigger of the spirit — and hardly anything else. Which sounds. . . well, I’m going to go with “adventurous”.
The U.S. ban on Absinthe was lifted in 2007.