This is, quite literally, the bark from several kinds of willow tree: white willow, pussy willow, crack willow, purple willow, and more. During Hippocrates’s time, people gnawed on pieces of the bark to relieve pain and fever. Turns out they were ahead of their time: The bark contains salicin, a chemical that acts an awful lot like aspirin. Today medical professionals use it to treat pain, from headaches and menstrual cramps to muscle pain and arthritis.

The Evidence

Although a wealth of research doesn’t exist (aspirin manufacturers have deeper pockets for studies), there’s decent evidence that willow bark reduces lower back pain after about a week of daily supplementation. Early research suggests that it can tamp down pain from osteoarthritis, while the results for rheumatoid arthritis are mixed.

“I prescribe willow bark in combination with other herbs for low back pain, rheumatoid arthritis, and other conditions of inflammatory joint and/or muscle pain,” says Janelle Louis, a functional medicine practitioner at Focus Integrative Healthcare in Overland Park, Kansas.

Like aspirin, willow bark may slow blood’s ability to clot, so taking it alongside blood thinners may up your chances of bruising and bleeding. “To experience maximum benefits from willow bark, it’s really important to make sure that you are taking an appropriate dosage and that you aren’t taking any medication that may interact with the herb,” Louis warns. “People taking anticoagulants like warfarin should especially exercise caution. Those taking NSAIDs, beta blockers, diuretics, and certain DMARDs including methotrexate should also speak with their physicians before taking willow bark.”

How to Use It

Research on patients with back pain has shown that 240 milligrams of salicin, willow bark’s active ingredient, effectively reduced symptoms. Check with your doctor before you buy a bottle of pills, though, because the natural drug isn’t for everybody. “I don’t recommend taking willow bark while breastfeeding because some of its constituents can be excreted into breast milk and can lead to sensitivities or allergies in your baby,” Louis says. “I also don’t usually recommend that children 17 and under take willow bark because of the potential risk of developing Reye’s syndrome, a serious complication of consuming salicylate-containing products—such as aspirin—when recovering from a virus such as the flu.”

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