Arnica: Benefits, Safety, and More

Arnica (Arnica montana) is an herb in the sunflower family (Asteraceae). It’s native to Europe and can be found in North America. Arnica plants have long, downy leaves, and the flowers are daisy-like. 

Arnica is typically used in topical (on the skin) homeopathic remedies that are diluted. Preparations are typically used to treat aches, pains, and bruises. Arnica is thought to contain anti-inflammatory compounds that relieve muscle and joint pain.

Arnica is poisonous in large amounts, especially if taken by mouth. It’s recommended to avoid taking arnica internally unless under the supervision of a healthcare provider. 

This article discusses the potential uses of arnica and the risk factors and side effects of taking arnica.

What Is Arnica?

Arnica (Arnica montana) is an herb used in herbal medicine and homeopathy for hundreds of years. The anti-inflammatory ingredient in arnica is called helenalin. This compound is toxic and can irritate the skin if not diluted.

Arnica can be applied topically to the skin as a gel, balm, cream, or ointment. Oral forms are also available as teas, tinctures, and tablets. Arnica is poisonous in large amounts. Avoid taking it by mouth. 

Arnica (Arnica montana) is not to be confused with arnica tea (i.e., Heterotheca inuloides, known as Mexican arnica) or Brazilian arnica (Solidago chilensis Meyen).

Purported Uses of Arnica

Supplement use should be individualized and vetted by a healthcare professional, such as a registered dietitian nutritionist (RD or RDN), pharmacist, or healthcare provider. No supplement is intended to treat, cure, or prevent disease.

Arnica is commonly used in complementary and alternative medicine. It has been researched for use in:

• Bruising
• Pain
• Myalgia, or muscle soreness
• Arthralgia, or aching joints

The plant can be toxic. Because of this, it is most often used in a homeopathic form. Homeopathic products contain very small amounts of the active ingredient.

Research on the potential health benefits of arnica is limited. There is NOT enough evidence to support its use for any of these conditions due to a lack of human research. More research is needed. Very few well-designed, placebo-controlled, peer-reviewed human studies have been published.

Osteoarthritis

Osteoarthritis is often referred to as "wear-and-tear" arthritis. In this condition, the cartilage that protects the joints wears down over time. It is often treated with nonsteroidal anti-inflammatory drugs (NSAIDs) or other pain relievers.

In one review of several studies, Australian researchers looked at seven trials of topical herbal remedies for osteoarthritis. Arnica gel appeared to work nearly as well as Advil (ibuprofen). Benefits included reduced and improved joint function in people with hand osteoarthritis.

However, in one of the seven trials, 13% of those who used arnica gel had side effects. This is compared to 8% of Advil users. Some even reported an increase in joint stiffness and pain.

More research is needed. Discuss with your healthcare provider about taking arnica for your osteoarthritis before starting this supplement.

Plastic Surgery Recovery

In a study published in 2016, topical (on the skin) Arnica montana appeared to speed up healing after rhinoplasty (plastic surgery of the nose). Bruises seemed less intense and to heal faster. However, the study was very small. Further study is needed.

Exercise Recovery

A study published in 2022 used a topical combination product with menthol and arnica to accelerate lower body recovery after exercise in males. The product purportedly increased the recovery rate and reduced muscle soreness following intense exercise. However, this was a combination product, so arnica’s effect alone can’t be validated. Also, the study was in males only, and the findings can’t be generalized to females.

What Are the Side Effects of Arnica?

Arnica is known to cause side effects. This is true even when used in very diluted topical ointments or creams. More serious side effects can occur with oral forms.

Topical Use

In less-diluted formulas, arnica may cause a mild allergic reaction. This happens most often in people allergic to plants of the Asteraceae family. These plants include:

• Ragweed
• Marigolds
• Chrysanthemums
• Daisies

Arnica can also trigger increases in blood pressure and heart rate. This is more likely if used in excess or on broken skin. More of the active ingredient can be absorbed through broken skin. On broken skin, arnica may also cause stinging.

Oral Use

Most homeopathic arnica remedies are very diluted. These are generally considered safe. Some forms, though, may contain detectable amounts of helenalin. These forms have health risks.

When taken by mouth, helenalin–an active part of arnica–can cause the following:

• Mouth and throat irritation
• Stomach pain
• Diarrhea
• Vomiting
• Shortness of breath
• Easy bruising and bleeding
• Rapid heartbeat
• High blood pressure

Avoid taking arnica internally unless under the careful supervision of a healthcare provider.

Precautions

Pregnant or lactating individuals and children should not take arnica in any form. Individuals allergic to ragweed and related plants (e.g., chrysanthemums, marigolds, daisies) who take arnica may have an allergic reaction.

It is also recommended to stop taking arnica two weeks before surgery, as it may cause extra bleeding before and after surgery.

How to Take Arnica

There is not enough scientific evidence to determine a standard or appropriate dose of arnica. More research is needed on dosages for specific health needs and populations.

What Happens if I Take Too Much Arnica?

Arnica can be toxic and potentially fatal if taken internally. As a rule of thumb, follow the manufacturer's recommended dosage. 

If you experience side effects of any kind, stop taking arnica and seek immediate medical attention.

Interactions

Avoid arnica if you are taking blood-thinning medication. The combination could increase your risk of bleeding and bruising.

Arnica may interact negatively with these medications:

• Jantoven (warfarin)
• Plavix (clopidogrel)
• Heparin
• NSAIDs, like ibuprofen and Naprosyn (naproxen)

Supplements that can slow blood clotting should also be avoided, such as garlic, ginger, ginkgo, and Panax ginseng.

It is essential to carefully read a supplement's ingredient list and nutrition facts panel to know which ingredients and how much of each ingredient is included. Please review this supplement label with your healthcare provider to discuss potential interactions with foods, other supplements, and medications.

Summary

Arnica is an herb believed to help relieve pain associated with arthritis and muscle soreness. It is available in topical and oral forms.

When it is undiluted, arnica may cause side effects like nausea, rapid heart rate, and bruising or bleeding. It may also interact with blood-thinning drugs. Always speak with your healthcare provider before taking arnica or any other supplement.