Willow bark has similar properties to aspirin and has been used historically for pain relief. It’s available as a supplement in various forms, but it isn’t regulated. The research on its effectiveness is contradictory.

Willow bark, the bark of several varieties of willow trees, has been used for centuries as a remedy for inflammation and pain.

Some people may use willow bark as an alternative to aspirin, particularly those who experience chronic headaches or back pain. Willow bark is also used in some products to aid weight loss.

Read on to learn about willow bark, how it may have similar properties to aspirin, and what the research says.

Willow bark comes from the branches of 2- to 3-year-old willow trees. Willow trees and shrubs grow worldwide, except in Australia and Antarctica.

Varieties of willow bark include:

  • Salix purpurea (purple willow)
  • Salix fragilis (crack willow)
  • Salix alba (white willow)
  • Salix daphnoides (violet willow)
  • Salix pentandra (bay willow)

The white willow and black willow are two of the most common willows that are used medicinally.

Along with various polyphenols, willow bark contains salicin. Salicin is a type of alcohol that contains a compound called β-glucoside. When you consume it, your body breaks it down into two parts: glucose and salicyl alcohol. The alcohol is then converted into salicylic acid through a process called oxidation.

Salicylic acid may be effective in reducing the production of prostaglandins, which cause inflammation and pain in the body.

In fact, salicylic acid is the most basic form of a group of chemicals known as salicylates. This is why it may have properties similar to aspirin, which breaks down quickly in the body into salicylic acid.

Historically, Native Americans chewed willow bark to relieve pain. Today, people may use willow bark to treat conditions like back pain, osteoarthritis, or muscle aches. It’s often found as an ingredient in various supplements.

That said, there’s still limited scientific evidence to support its effectiveness in treating these ailments.

Here’s what the research says:

Arthritis

In a 2023 research review looking at 329 patients with different types of arthritis, researchers found that people who used willow bark had more symptom relief than those who took a placebo.

But in older research examining the effects of willow bark extract on people with osteoarthritis (OA) and rheumatoid arthritis (RA), they found inconclusive results.

Some studies found no difference in pain relief compared to a placebo or medication, while others showed minor improvements that did not reach statistical significance.

It’s worth noting that most types of arthritis are inflammatory conditions. When it came to studies on pain caused by musculoskeletal conditions like osteoarthritis or general back pain, researchers found more improvement in pain with mild to minimal side effects in most cases.

In these cases, the differences in findings may have been related to the specific formulation, the type of willow bark, or the dose.

Antimicrobial properties

A 2021 study suggests that two willow bark extracts may have significant anti-inflammatory effects on strings of amino acids called peptides and inflammatory cells produced by COVID-19.

Yet more research is needed to understand whether this means willow bark can actually reduce viral inflammation, such as fever.

In another 2021 study, researchers examined 16 different types of northern willow trees to see how they could be used for natural products using a gentle hot water extraction technique.

The results found that all types may have antiviral effects against viruses such as coxsackievirus A9 and bacteria like Staphylococcus aureus and Escherichia coli (E. coli). They didn’t appear to be as effective against fungi.

The findings weren’t exactly the same depending on the type of bark, and more research is necessary to replicate these findings in people.

Skin aging

A 2024 test-tube study looked at certain polyphenols found in a type of willow bark, Salix chaenomeloides, on human skin cells.

The results suggest the potential for reducing skin aging from sun damage and inflammation while promoting antioxidant activity, though clinical studies on human subjects are needed to verify this finding.

Weight loss

Willow bark is often an ingredient in dietary supplements — which are not regulated by the FDA.

In fact, there’s very limited evidence that the plant is effective in this space. More research is needed to determine the effect of any species of willow bark on human weight.

When taken in moderation, willow bark does not appear to have negative side effects. Too much willow bark, however, can cause stomach cramping and bleeding.

Other rarer side effects may include:

It may also cause heavy metal poisoning, as some species may accumulate heavy metals from their environment.

In some cases, you could develop an allergic reaction to willow bark, which can become life threatening. Some cases of anaphylaxis have been reported. If you have a known allergy to aspirin, you’re at a particular risk.

Anaphylaxis

Anaphylaxis is a severe reaction to a trigger, such as an allergy, and is potentially life threatening.

Symptoms can develop quickly and include:

  • feeling faint or lightheaded
  • difficulty breathing or wheezing
  • rapid heartbeat
  • confusion
  • anxiety
  • clammy skin
  • collapsing or losing consciousness
  • hives
  • swelling
  • stomach pain, nausea, or vomiting

If you or someone nearby develops these symptoms, you should:

  1. Check to see whether they have an epinephrine pen. If they do, read and follow the instructions to dispense the medication.
  2. Dial 911 or a local emergency number.
  3. Lay them down. If they have vomited, lay them on their side.
  4. Stay with them until emergency services arrive.

It is possible for someone to need more than one injection with an epinephrine pen. If symptoms do not begin to clear after 5 minutes, give a second injection if one is available.

Willow bark can also interact with certain medications, such as blood thinners and beta-blockers, and even acetaminophen (Tylenol), which in at least one case was associated with the development of Reye’s syndrome.

Children and adolescents up to the age of 16 are particularly at risk of Reye’s syndrome and should avoid willow bark.

People who are pregnant or breastfeeding are also discouraged from taking any medication that contains salicylates.

People with gastric ulcers should also be especially careful with willow bark, in the same way they would be cautious with aspirin because too much could cause stomach bleeding.

Willow bark is available as a supplement in various forms. These include capsules, which can be purchased from many drugstores and almost any health food store.

Based on research studies, the recommended dose for pain relief is 240 milligrams (mg) a day.

Willow bark can be used topically as an ingredient in creams or other skin care products. Other forms include:

  • chewing the bark
  • taking it in tincture form
  • drinking it as tea

With these methods, it’s hard to tell how much you’re getting in each serving.

Because willow bark could accumulate heavy metals, and there’s no way to know how much has accumulated in the extract you’re choosing to use, you should approach any supplement with extreme caution.

Willow bark has been shown to help relieve some mild discomfort. But more research is needed to fully understand how it differs from aspirin and whether it’s truly effective for various types of ailments in people.

While it may be an effective alternative to aspirin for some, talk with a doctor before using willow bark.