Overview

Willow bark comes from willow trees and contains a chemical called salicin. Salicin is used to make aspirin. It works similarly to aspirin in your body, so willow bark is commonly used for aches and pains and to reduce fever. Common side effects include nausea, vomiting, diarrhea, heartburn, stomach pain, and rash. Before taking willow bark, make sure to tell your health care provider about any health conditions you have or medicines you are taking.

Uses

What is willow bark used for?

Willow bark is used for aches and pains and to reduce fevers. Although it may be used for other reasons, its benefits for other uses are not well defined.

Note: The FDA has not reviewed willow bark for safety and effectiveness. Learn more about dietary supplements here.

How does willow bark work (mechanism of action)?

Willow bark comes from willow trees, which are called salix trees. Willow bark contains a chemical called salicin that is used to make aspirin (salicylic acid). Most willow bark dietary supplements contain the dried bark of certain willow species, including Salix nigra, S. alba, S. cortex, and S. lucida.

The salicin in willow bark is very similar to aspirin and works in the same way to block substances in the body that can cause pain, swelling (inflammation), and fever. As a result, willow bark supplements are commonly used for many of the same reasons as aspirin. But aspirin is made in a lab, and each aspirin tablet is standardized to contain the same amount of the drug. Willow bark, on the other hand, is a natural product that contains variable amounts of salicin. Each willow bark product or batch may contain different amounts of salicin, which can change its effects and side effects.

Willow bark also contains many other chemicals. The amounts of each chemical in a specific willow bark product may vary. Some, none, or all of these chemicals may have effects on the body. These effects may change depending on how much of each chemical is found in the product you are using.

How should I store willow bark?

You should store willow bark according to the product label. Most dietary supplements should be kept in a cool, dry location that is out of the reach of children and pets and not in direct sunlight.

Side Effects

What are the most common side effects of willow bark?

The most common side effects of willow bark are listed below. These side effects may vary depending on the dose you are taking or the specific product you are using. Tell your health care provider if you have any of these side effects that bother you.

• Diarrhea
• Heartburn
• Nausea or vomiting
• Rash

There may be other side effects of willow bark that are not listed here. Contact your health care provider if you think you are having a side effect of a supplement. In the U.S., you can report side effects to the FDA at www.safetyreporting.hhs.gov or by calling 888-SAFEFOOD (888-723-3366). In Canada, you can report side effects to Health Canada at www.health.gc.ca/medeffect or by calling 866-234-2345.

What are the serious side effects of willow bark?

While less common, the most serious side effects of willow bark are described below, along with what to do if they happen.

Severe Allergic Reactions. Willow bark may cause allergic reactions, which can be serious. Stop taking willow bark and get help right away if you have any of the following symptoms of a serious allergic reaction.

• Breathing problems or wheezing
• Racing heart
• Fever or general ill feeling
• Swollen lymph nodes
• Swelling of the face, lips, mouth, tongue, or throat
• Trouble swallowing or throat tightness
• Itching or skin rash
• Bumps on the skin called hives that can be red, pink, white, or brown depending on your skin tone
• Nausea or vomiting
• Dizziness, feeling lightheaded, or fainting
• Stomach cramps
• Joint pain

Stomach Bleeding.Willow bark can increase your risk for bleeding, ulcers, and tears (perforation) in your gut. The risk is higher if you take higher doses of willow bark than recommended on the label, have poor health, are 60 or older, drink alcohol, or take certain other medicines. The risk may also be higher if you have a history of stomach ulcers, bleeding problems, liver disease, or smoking. Stop taking willow bark and get emergency help if you have any of the following symptoms.

• Vomit blood
• Black or tarry poop
• Stomach pain that does not go away
• Upset stomach
• Feel faint

Reye’s Syndrome. Children or teenagers who have chickenpox, the flu, or flu-like symptoms should not take willow bark. Taking willow bark to treat an infection caused by a virus can lead to Reye’s syndrome. If your child or teenager is taking willow bark and has changes in their behavior, nausea, and vomiting, contact your health care provider. These may be early signs of Reye’s syndrome.

Precautions

Who should not use willow bark?

Allergies to Ingredients. People who are allergic to any of the following should not take willow bark.

• Aspirin
• Salicin
• Salicylates
• Willow bark
• Any other medicine known as a pain reliever or fever reducer
• Any of the ingredients in the specific product

Your pharmacist can tell you all of the ingredients in the specific willow bark products they stock.

What should I know about willow bark before using it?

Willow bark is a dietary supplement. It cannot be marketed to treat or cure a disease.

Read and follow the directions on the specific product you are taking, or take it as recommended by your health care provider.

Keep willow bark out of the reach of children.

Taking willow bark with food and a full glass of water may help reduce your risk of having stomach-related side effects.

People who are 60 or older can be at greater risk of some side effects from willow bark. Talk to your health care provider about your risks if you are in this age group.

If you are taking willow bark for pain, call your health care provider if your pain is getting worse, the painful area is also red or swollen, or the pain lasts longer than 10 days.

If you are taking willow bark for a fever, call your health care provider if your fever gets worse or lasts longer than three days or you get a severe headache.

Herbal products, such as willow bark, naturally contain many chemicals. The amount of each chemical in a specific willow bark product can change for many reasons, including the area where the tree was grown, the weather during growth, the time of year when it was harvested, and the way that the bark was processed after it was harvested. If you switch to a new bottle or a different brand, you may not have the same effects or side effects because of this variability. Talk to your health care provider if you have questions or concerns.

Willow bark is available in many forms, including a tea, liquid extract, capsule, and dried and ground powder. Each of these forms may contain different amounts of the chemicals that are naturally found in the bark.

If you are taking willow bark powder, use an appropriate measuring device to measure the powder, such as the device included with the product. If you are taking a liquid product, use an accurate measuring device to measure your dose. A household spoon is not an accurate measuring device and may cause you to take the wrong dose. Read the product label carefully and follow the instructions on the label.

Some willow bark products have been found to contain heavy metals, which can cause serious health problems. The FDA has not tested willow bark products to confirm that they contain the ingredients stated on their labels. Some dietary supplements have been tested by third-party organizations to confirm that they contain the ingredients listed on their labels and do not contain any harmful chemicals. Learn more about how to choose a safe dietary supplement product here.

What should I tell my health care provider before using willow bark?

Tell your health care provider about all of your health conditions and any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using. This will help them know if willow bark is right for you.

In particular, make sure that you discuss any of the following.

Current and Past Health Conditions.Tell your health care provider if you have any of the following.

• Asthma
• Bleeding problems
• Glucose-6-phosphate dehydrogenase (G6PD) deficiency
• Kidney or liver problems
• Stomach ulcer
• Drink alcohol regularly

Other Medicines and Supplements.Willow bark may interact with other medicines and supplements. Before taking willow bark, tell your health care provider about any prescription or OTC medicines, vitamins/minerals, herbal products, and other supplements you are using. See the Interactions section for more details.

Pregnancy. Willow bark may cause harm to the baby and lead to complications during pregnancy, especially if it is taken at 20 weeks or later in pregnancy. Tell your health care provider if you are pregnant or plan to become pregnant.

Breastfeeding. Willow bark passes into breast milk. Tell your health care provider if you are breastfeeding or plan to breastfeed. Your health care provider will let you know if you should stop breastfeeding or stop taking willow bark.

Interactions

Does willow bark interact with foods or drinks?

There are no known interactions between willow bark and foods or drinks. But taking willow bark with food might help reduce the risk of having side effects.

Drinking alcohol regularly may increase your risk for side effects with willow bark. It is best to limit the amount of alcohol you drink.

Does willow bark interact with medicines (drug interactions)?

Always tell your health care provider about any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using.

In particular, make sure that you discuss if you are using any of the following before taking willow bark.

• A blood thinner, which is a medicine used to treat or prevent blood clots
• A nonsteroidal anti-inflammatory drug (NSAID), such as ibuprofen, naproxen, and others, which is in many prescription and OTC products for pain, swelling, and fever
• A corticosteroid, such as dexamethasone, methylprednisolone, or prednisone, which is a medicine for certain inflammatory conditions
• A medicine for arthritis
• Aspirin, which is in many prescription and OTC products, including those for pain, swelling, and fever
• Methyl salicylate, which is a medicine that is applied to the skin for pain and swelling

The interactions between willow bark and medicines are not fully understood. As with most dietary supplements, the research on drug interactions with willow bark is incomplete. Always check with your health care provider before taking willow bark with any medicines.

Dosing

What should I do if I accidentally use too much willow bark?

If you or someone else has used too much willow bark, get medical help right away, call 911, or contact a Poison Control center at 800-222-1222.

Willow bark comes in many forms that contain a wide range of doses. It is usually taken only when needed. Read the product label closely, and speak with a health care provider about how to take willow bark safely. Do not take double or extra doses, even if you miss a dose.