Palo azul is a tree native to Mexico whose bark and wood are brewed into a tea that glows blue under light. Known scientifically as Eysenhardtia polystachya, it has been used in Mexican traditional medicine for centuries, primarily to support kidney health. Its English common name, kidneywood, reflects that long history. The tea remains popular today across Mexico and the southwestern United States, sold as dried bark chips in herbal shops and online.
The Tree and Its Blue Glow
Eysenhardtia polystachya is a deciduous tree or shrub that grows 3 to 9 meters tall with a trunk diameter of 15 to 35 centimeters. It has rough, scaly bark that’s dark on the outside and reddish-brown on the inside, with compound leaves made up of small elliptical leaflets. The wood contains aromatic resins. Across different regions of Mexico, the tree goes by many names: palo dulce (sweet wood), coatillo, taray, and vara dulce, among others.
The most striking feature of palo azul tea is its fluorescence. When you steep thin pieces of the bark in water, the liquid develops a distinctive blue shimmer, especially visible when light hits it at an angle. This isn’t a dye or pigment. The bark contains a specific group of flavonoids that evolved to protect the tree against UV radiation. These compounds absorb high-energy ultraviolet light and re-emit it as lower-energy blue light, creating that characteristic glow. The name “palo azul” translates directly to “blue stick” or “blue wood.”
A Long History in Traditional Medicine
Palo azul’s medicinal use dates back to pre-Hispanic cultures in Mexico. The earliest written record comes from 1565, when Spanish physician Nicolas Monardes described a tree used to treat kidney and urinary diseases. He noted that people drank a blue-colored infusion made by placing thin slices of bark into water and letting them soak. That basic preparation method has barely changed in nearly 500 years.
Kidney Health and Stone Prevention
The traditional claim that palo azul supports kidney function has some backing from animal research, though no human clinical trials have been conducted on the tea itself. In animal studies, the plant’s compounds appear to work through three mechanisms: antioxidant effects that protect kidney cells from damage caused by unstable molecules, anti-inflammatory activity that reduces irritation in the urinary tract, and a mild diuretic effect that increases urine flow.
That diuretic property is key to its reputation as a kidney remedy. By increasing the volume and frequency of urination, the tea may help flush out the crystal-forming compounds that eventually become kidney stones, washing them away before they can grow large enough to cause problems. The antioxidant compounds also appear to interfere with the early stages of stone formation and growth, at least in laboratory settings. These effects are plausible and consistent with how other plant-based diuretics work, but until researchers test the tea in human trials, the evidence remains preliminary.
Blood Sugar and Metabolic Effects
Palo azul has also been traditionally used in parts of Latin America for managing diabetes. Animal research offers some clues about how this might work. In one study, mice fed a high-fat diet and given palo azul extract showed changes in fat cell development and muscle cell maturation that are associated with improved insulin sensitivity. The extract appeared to activate a key regulator of fat cell differentiation and boost a cellular energy sensor called AMPK in muscle cells, both of which play roles in how the body processes sugar and responds to insulin.
At a dose of 250 mg/kg in mice, the extract showed a tendency to reduce fat tissue volume while increasing the expression of adiponectin, a hormone that helps regulate blood sugar. It also promoted the formation of mature muscle fibers, which are the body’s primary consumers of glucose. These findings suggest a real biological mechanism behind the traditional use, but the leap from mouse studies to reliable human effects is a large one.
What’s Actually in the Bark
Researchers have isolated at least 13 distinct compounds from the bark, including six previously unknown flavonoids. The bark is rich in polyphenols, the same broad class of plant compounds found in green tea, berries, and dark chocolate. The specific types found in palo azul include chalcones, isoflavones, and coumarins, each with slightly different biological activities. This chemical diversity likely explains why the tea has been used for such a range of purposes in folk medicine.
The flavonoids are responsible for both the tea’s fluorescent blue color and most of its proposed health effects. These compounds act as antioxidants, neutralizing the reactive molecules that damage cells throughout the body. Some of the isolated compounds also showed antimicrobial activity against common bacteria like E. coli in lab tests, with effective concentrations as low as 1.56 micrograms per milliliter.
How to Prepare Palo Azul Tea
The traditional method is straightforward. You add pieces of dried bark (typically sold as chips or shavings) to water and boil them for anywhere from 15 minutes to over an hour. Longer steeping produces a stronger brew with more visible fluorescence. The tea itself tastes mild and slightly woody, without the bitterness common to many herbal teas. Some people drink it warm, others chill it and drink it cold throughout the day.
There is no standardized dosage. Traditional preparations vary widely, and without human clinical trials, no evidence-based recommendation exists for how much to drink or how often. The bark is sold in bags of varying weights, and preparation instructions differ between sellers.
Palo Azul and Drug Tests
One of the most common reasons people search for palo azul is the widespread claim that drinking the tea can help you pass a drug test. This belief likely stems from its diuretic effect: by increasing urine output, the idea is that it dilutes or flushes out detectable substances. There is no scientific evidence supporting this claim. No studies have tested whether palo azul tea affects the concentration of drug metabolites in urine, and its diuretic effect is mild compared to simply drinking large amounts of water. Any perceived benefit is almost certainly due to the extra fluid intake rather than a unique property of the tea itself.
Safety Profile
Toxicity testing in animal models suggests palo azul has a favorable safety profile. An ethanol extract of the branches and leaves showed low toxicity in both cell-based and animal tests, with a lethal dose threshold above 2,000 mg/kg in mice (administered both orally and by injection). That’s a wide safety margin. The extract also showed no toxic effects on human cells at concentrations up to 300 micrograms per milliliter in lab settings, and it did not damage DNA in human immune cells at concentrations below 200 micrograms per milliliter.
That said, these results come from controlled laboratory conditions using standardized extracts, not from the variable concentrations you’d get brewing bark at home. The safety of palo azul during pregnancy and breastfeeding has not been established. Because it has diuretic properties, drinking large amounts could theoretically affect hydration or interact with medications that influence fluid balance or kidney function.