It's a supplement

A number of places, Houston included, have laws that forbid the selling of alcohol on a Sunday. The roots of this legislation of course stems from the Christian practice of making Sunday a day of worship, and that somehow restricting the ability to purchase booze will promote propriety. Which is, of course, unrealistic in the modern age of refrigeration and super mega warehouse clubs where folks can buy more than enough to tide them over a day - it is only an inconvenience to the purveyors.

Unless, of course, you're selling a supplement.

No, not made from vampires and werewolves. Be sure to look for the utility belt, though.

Underberg is readily available in local supermarkets, sold alongside the various import items like spaetzle mix and licorice. It is purported to be an herbal aid to digestion, in single serving bottles of about 20ml. And is 44% alcohol. For those of you uncertain in your chemistry, this stuff is 88 proof. That's higher than vodka.

Of course, classified as a supplement, the "natural" (this term itself is meaningless) stuff can also be marketed with claims of various health effects, without need for basic science backing it up. It's a product that can exist in a number of loopholes both in marketing and availability.