Lettuce water was likely inspired by a 2017 study in the journal Food Science and Biotechnology, conducted by researchers in Korea. This study did find that compounds in romaine lettuce had a relaxing effect, but Stacie J. Stephenson, DC, functional medicine practitioner and author of Vibrant: A Groundbreaking Program to Get Energized, Own Your Health, and Glow, notes a few important caveats: This research was conducted on mice, and it was done using isolated plant compounds.
“According to the actual science, it is the lactucin and lactucopicrin, so-called phytochemicals or compounds found in plants, in lettuce that seem to be the ‘active ingredients,’ as they have a demonstrated analgesic (pain-relieving) effect similar to ibuprofen, as well as a sedating effect. When dosed with the lactucin-containing extracts, mice fell asleep significantly sooner and slept significantly longer than the controls,” Stephenson told mbg after digging into the research. However, she adds, “that’s mice, not people.”
Furthermore, the extracts used in this experiment were prepared using a lengthy drying, powdering, and extraction process to preserve potency. Simply popping lettuce in boiling water won’t necessarily have the same effect.
“It’s unlikely the compounds in lettuce tea reach the levels of the extracts used in research studies,” registered dietitian Abby Cannon, J.D., R.D., CDN suspects. “It’s also unclear whether those compounds enter the water itself or if they remain in the lettuce, and whether those extracts change when exposed to heat.”
Stephenson also notes that other research (again, not done on humans) has found that lettuce extract combined with other herbs like skullcap can increase time spent in REM sleep. But it’s unclear how much of that is due to the lettuce, and how much is the skullcap—which is more often used as a sedative. However, she does add that lettuce seed oil has long been prized as a sleep aid in Korea, so it’s possible that science is still catching up to this traditional medicine.