Herb & supplement monograph

Willow Bark Drug Interactions, Uses, Effectiveness, Safety & More

Medically reviewed by Dr. Brian Staiger, PharmD, BCPS ·Updated July 2026

What is this page for?

First and foremost: how Willow Bark interacts with medications. The heart of this page is the interaction list — every drug Willow Bark is known to interact with, and how serious each one is.

But these pages have grown well beyond that into a full monograph — what Willow Bark is, what people use it for and how strong the evidence is, its safety and side effects, and answers to the questions we’re asked most — written and reviewed by the clinical staff at HelloPharmacist. It’s educational information from our licensed clinical databases, not medical advice, and we don’t sell or endorse products. Our editorial policy

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Willow Bark Drug Interactions: The Bottom Line

From the HelloPharmacist Editorial Team · Updated July 2026

Based on the available evidence, Willow Bark drug interactions are all rated moderate rather than major, so while none are considered dangerous for most people, a few combinations deserve genuine caution, especially blood thinners. No interaction is rated major, and nearly all of the concerns trace back to one thing: willow bark contains salicin, a natural compound that acts like a mild dose of aspirin.

Interactions deserving the most attention

The combinations that matter most involve bleeding risk. Pairing willow bark with anticoagulant or antiplatelet drugs could add to their blood-thinning effect, since willow bark itself mildly reduces platelet activity. Taking it alongside aspirin or other salicylate medicines, such as salsalate or choline magnesium trisalicylate, may stack similar effects and side effects. There is also a less-documented concern that willow bark could raise levels and side effects of acetazolamide, based on limited human reports.

What the rest of the list means

A long list of interacting medications does not mean each one is proven harmful. Most entries reflect the same predicted concern, that willow bark's aspirin-like compound could add to the effects of blood-thinning or salicylate drugs, rather than separate documented problems. These effects are largely theoretical, and willow bark's antiplatelet action appears weaker than aspirin's.

Check your medications against Willow Bark

Based on HelloPharmacist’s Willow Bark interaction data and reviewed under our editorial standards.

Interaction report

Drugs that interact with Willow Bark

127 medications have a known interaction with Willow Bark, graded by severity. Select any drug for the full evidence-based detail.

Don’t want to scroll the list? Just ask.

Tell us the medications you take and we’ll check each one against Willow Bark using our pharmacist-reviewed interaction data.

AI summaries are generated from our Willow Bark interaction data for education only — always confirm with your pharmacist. How we use AI

2,830 drugs

Read The List Like a Pharmacist

What Severity, Likelihood & Evidence Mean

Severity — How Serious It Can Be

Major. Clinically significant; generally best avoided, or used only under direct professional supervision.
Moderate. May need monitoring, a dose adjustment, or separating the times you take each one.
Minor. Generally not clinically significant, but still worth noting and mentioning to your pharmacist.
No known interaction. Checked against our sources with nothing documented — not the same as proven safety.

Likelihood — How Well It’s Documented

Likely. Well-controlled human studies have demonstrated the likely existence of this interaction
Probable. Interaction has not been documented in well-controlled studies, however, the interaction has been demonstrated in some small human studies or in controlled animal studies in conjunction with multiple case reports.
Possible. Interaction has been documented in animal or in lab research, or the interaction has been documented in humans but is limited to case reports or conflicting clinical research exists
Unlikely. Interaction has been demonstrated in animal or in lab research but has been shown not to occur in humans.

Where This Data Comes From

Interaction records are evidence-graded and sourced from the Natural Medicines database (TRC Healthcare), the same reference used by pharmacists and hospitals.
Each drug listed above links to the full report for that exact Willow Bark combination — clinical detail, likelihood, evidence level, and citations.
Content is reviewed by licensed HelloPharmacist pharmacists — see our data sources and editorial standards.

The big picture

The kinds of drugs Willow Bark affects

Every type of medication (drug category) Willow Bark is known to interact with. Open any category for the detail — or search your exact drug in the checker above.

All 5 drug categories Willow Bark interacts with

AcetazolamideAnticoagulant/antiplatelet DrugsAspirinCholine Magnesium Trisalicylate (trilisate)Salsalate (disalcid)

Acetazolamide

Theoretically, willow bark might result in additive adverse effects associated with acetazolamide.
Willow bark contains salicin, a plant salicylate. Human case reports suggests that a combination of acetazolamide and salicylate increases unbound plasma levels of acetazolamide, as well as adverse effects related to acetazolamide.

Likelihood Possible Evidence D

Anticoagulant/Antiplatelet Drugs

Theoretically, willow bark might increase the risk of bleeding when taken with anticoagulant/antiplatelet drugs.
Willow bark has antiplatelet effects, but less so than aspirin.

Likelihood Probable Evidence D

Aspirin

Theoretically, willow bark might increase the effects and adverse effects of aspirin.
Willow bark contains salicin, a plant salicylate. It might have an additive effect when taken with other salicylate-containing drugs such as aspirin.

Likelihood Probable Evidence D

Choline Magnesium Trisalicylate (Trilisate)

Theoretically, willow bark might increase the effects and adverse effects of choline magnesium trisalicylate.
Willow bark contains salicin, a plant salicylate. It might have an additive effect when taken with other salicylate-containing drugs such as choline magnesium trisalicylate.

Likelihood Probable Evidence D

Salsalate (Disalcid)

Theoretically, willow bark might increase the effects and adverse effects of salsalate.
Willow bark contains salicin, a plant salicylate. It might have an additive effect when taken with other salicylate-containing drugs such as salsalate.

Likelihood Probable Evidence D

Monograph

Willow Bark: Uses, Safety & Side Effects

Medically reviewed by Dr. Brian Staiger, PharmD, BCPS · Reviewed July 2026 ·

The bottom line

Willow bark is a traditional plant remedy that contains salicin, a compound related to aspirin, and is most often used for pain and inflammation. Some evidence suggests it may modestly help low back pain and joint pain, but the research is limited and the right dose is not well standardized. Because it acts like aspirin, people with aspirin allergies, bleeding problems, or who are pregnant should be cautious and talk to a pharmacist or doctor first.

Scientific name: Salix alba
Family: Salicaceae
Part used: Bark
Common forms: Capsules, tablets, dried bark for tea, liquid extracts, standardized extracts

People commonly use it for

Low back pain
Osteoarthritis joint pain
Headache
Fever
General aches and inflammation

Popular and traditional uses — not proof it works. See “Uses & effectiveness” below for the evidence.

Safety at a glance

OverallUse caution

Generally tolerated short-term by healthy adults, but it acts like aspirin and is not safe for everyone.

PregnancyInsufficient reliable information

Insufficient reliable information available; avoid using.

Read the full pregnancy detail

BreastfeedingPossibly Unsafe

When used orally. Willow bark contains salicylates which are excreted in breast milk and have been linked to adverse effects in breast-fed infants.

Read the full breastfeeding detail

Pregnancy & breastfeeding ratings are from Natural Medicines (Therapeutic Research Center). Safety guidance is general; always confirm with your pharmacist or doctor for your situation.

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Overview

Willow bark comes from the bark of several willow trees, most commonly the white willow (Salix alba). Willows grow in many parts of Europe, Asia, and North America, often near rivers and wet ground.

People have used willow bark for thousands of years to ease pain and lower fever. It is famous for containing salicin, a natural compound that is chemically related to aspirin. In fact, willow bark helped inspire the discovery of aspirin in the 1800s.

Today it is sold as capsules, tablets, teas, and liquid extracts. It is most often used for back pain, joint pain, headaches, and minor aches.

How it works

The main active compound is salicin. After you swallow it, the body converts salicin into salicylic acid, which is closely related to the active form of aspirin.

Salicylic acid is thought to reduce pain and inflammation by lowering the body's production of certain chemicals called prostaglandins. Willow bark also contains other plant compounds, such as flavonoids and tannins, that may add antioxidant or anti-inflammatory effects.

Much of this understanding comes from the known action of aspirin and from laboratory studies. Because willow bark releases salicylic acid more slowly than aspirin, some believe it is gentler on the stomach, but this has not been firmly proven.

Effectiveness

Does Willow Bark work?

Here’s what the research actually shows for each use — graded by Natural Medicines and reviewed by Dr. Brian Staiger, PharmD.

Evidence overview · 12 uses evaluated

1 Possibly effective 11 Insufficient evidence

How to read these evidence grades

Natural Medicines’ 7-point scale. We show each rating’s label word-for-word.

1EffectiveStrong, consistent evidence it works.

2Likely EffectiveGood evidence, though not yet conclusive.

3Possibly EffectiveSome evidence suggests a benefit.

4Possibly IneffectiveSome evidence it may not help.

5Likely IneffectiveFairly strong evidence it doesn’t help.

6IneffectiveStrong evidence it doesn’t work.

7Insufficient Reliable Evidence to RateToo little research to say either way.

Possibly Effective Back pain