The human gut microbiome contains up to one thousand species of bacteria that, among many functions, produce neurotransmitters and hormones—including an estimated 90 percent of the body’s serotonin, the “feel-good” hormone that shapes your overall sense of well-being. It’s why scientists often refer to the gut as a “second brain,” influencing everything from digestion to metabolism, anxiety, and allergies, and explains the constant spate of probiotic supplements on the market today, whether kombucha, apple cider vinegar tonics, or trendy juice cleanses.

Though relatively new to North America, kōso, a century-old Japanese drink, is making a foray into the scene with R’s Koso, a direct-to-consumer start-up based in Los Angeles. Brewed in Japan and made from more than 100 different fermented raw, vegan ingredients and their natural enzymes, the beverage contains probiotics, prebiotics, and postbiotics—a combination said to improve gut health, and, it would follow, boost skin and mental health. To try it out, the company recommends adding a tablespoon or two of the sweet, plum-like elixir into a glass of still or sparkling water; or mixing it straight into your morning yogurt, milk, or even a cocktail.