What Is Arnica?

Arnica is an herb. It is in the sunflower family (Asteraceae).

Several species of Arnica contain an anti-inflammatory compound. This is thought to relieve pain, aches, and bruising. It is usually applied topically to the skin. Oral forms are also available.

This article discusses arnica, its uses, side effects, and preparation. It also looks at some of the research into its effectiveness.

What Is Arnica?

Arnica comes from the sub-alpine regions of western North America. It can also be found in arctic regions of Europe, Asia, and North America.

Arnica plants have long, downy leaves. Their flowers are daisy-like. They are bright yellow or orange and between 2 and 3 inches wide.

The anti-inflammatory ingredient in arnica is called helenalin. This compound is very toxic when consumed. It can also irritate the skin if it is not diluted.

Arnica is often sold as an over-the-counter (OTC) topical ointment, gel, or cream. It is also sold as a homeopathic topical application or oral pellet. Homeopathic remedies are highly diluted.

Other forms include:

• Extracts
• Tinctures
• Oral supplements
• Powders
• Aromatherapy oil
• Dried "wild-crafted" herb
  

What Is Arnica Used For?

Arnica is commonly used in alternative medicine. It is claimed to treat:

• 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 an active ingredient.

Arnica is sold by homeopathic drug makers. It is used for a number of conditions, including:

• Osteoarthritis
• Post-shingles neuralgia
• Diabetic neuropathy
• Post-surgical pain
• Wound healing
• Cancer

There is limited evidence to support arnica's use in treating any condition. This does not necessarily mean it does not have benefits. It just means that clinical studies have so far been small and poorly designed. Many have contradictory findings.

Talk with a doctor before deciding if arnica is a safe option for you.

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).

Arnica is thought by some to be a safe, natural alternative to NSAIDs.

In a 2013 review, Australian researchers looked at seven trials on topical herbal remedies for osteoarthritis.

Arnica gel appeared to work nearly as well as Advil (ibuprofen). Benefits included reducing pain and improving joint function in people with hand osteoarthritis.

However, 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.

Post-Surgical Pain and Bruising

Proponents of arnica think it can reduce bruising and swelling after surgery. For this use, it is either applied topically or taken as an oral supplement.

A 2016 review suggested that the arnica species A. montana was a "valid alternative" to NSAIDs in treating:

• Post-operative pain
• Edema or swelling
• Ecchymosis or bruising

Reviewers did state, though, that the results varied based on formulation and dosage.

Another review concluded there wasn't enough evidence to support the use of oral or topical arnica for swelling or bruising after surgery.

Muscle Pain

Muscle pain is also called myalgia. It is associated with a wide range of medical conditions. It can also happen after simple overuse of the muscles.

Most studies on arnica have focused on post-exercise muscle pain. Arnica has long been used for this purpose in sports supplements. Even so, there is little evidence to support its use.

One review of studies strongly endorsed the combined use of oral and topical arnica for muscle injuries.

The authors came to this conclusion even though four studies in the review found no benefits compared to a placebo. A placebo is a substance that contains no active ingredients. 

Possible Side Effects

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 can cause:

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

Contraindications and Interactions

In theory, arnica could slow blood clotting. Use of any non-homeopathic arnica should be discontinued two weeks before surgery. This will reduce the risk of postoperative bleeding.

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

These drugs include:

• Coumadin (warfarin)
• Plavix (clopidogrel)
• Heparin
• NSAIDs like ibuprofen and naproxen

Little is known about the safety of arnica during pregnancy. If you are pregnant or breastfeeding, ask your doctor before using arnica in any form.

Selection, Preparation, and Storage

Arnica montana is the species most often used for medical purposes. Chamissonis, A. longifolia, and A. gracilis are also sometimes used.

Most OTC arnica is very diluted. This results in gels, ointments, and extracts with little to no helenalin. This is also true for arnica powders, capsules, and other oral forms.

When purchasing arnica, look for brands that have been tested by an independent certifying body, such as:

• U.S. Pharmacopeia (USP)
• ConsumerLab
• NSF International

This way, you can be sure the product label is accurate. You will also be able to tell if there is any helenalin in the product.

Also make sure the Latin name of the arnica species (such as Arnica montana) is on the product label. Be wary of any product that claims to contain "pure arnica."

Most arnica preparations can be stored at room temperature. As a general rule, store them in their original containers. Keep them away from direct sunlight.

Never use more than the dose listed on the product label. Discard any arnica that is past its expiration date.

Summary

Arnica is an herb commonly used to treat pain. There is limited evidence to support its use.

Arnica is believed to help relieve pain associated with arthritis and muscle soreness. It is also used to treat post-surgical swelling and bruising. 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 ask a doctor before using any natural remedy. Look for arnica that is diluted and has been tested by a third party.

A Word From Verywell

Herbal remedies aren't subject to the same regulatory standards as pharmaceutical drugs. Be cautious when using any such product. Always ask your doctor before trying any of these remedies.

Remember that even natural products can be dangerous. They may cause unwanted side effects or interact with other drugs or supplements.