Methylsulfonylmethane (MSM)

By Rania Gollakner, BS, DVM, MPH

What is methylsulfonylmethane?

Methylsulfonylmethane (MSM) is a naturally occurring supplement used primarily as an anti-inflammatory and antioxidant for conditions such as arthritis and some cancers. MSM is used most often in dogs and horses, although cats may benefit as well.

"MSM is used most often in dogs and horses, although cats may benefit as well."

Dietary supplements are substances that can be used to supplement the diet, such as vitamins, minerals, amino acids, herbs, botanicals, enzymes, and probiotics. While many supplements are sold over the counter, they still contain ingredients that have biological effects that should be managed by your veterinarian. Follow your veterinarian’s directions and cautions very carefully as their directions may be significantly different from those on the label.

There are differences in how countries regulate supplements. In the United States, these substances are not as vigorously regulated by the FDA as other medications, which means they can be sold without the manufacturer proving their effectiveness, safety, and without a guarantee of consistent or accurately reported ingredients. In Canada, products that have been evaluated for quality, safety, and effectiveness by Health Canada and authorized for sale will have a license number on the label.

How effective is MSM?

Limited studies in companion animals have been performed and results are mixed, but there is some anecdotal evidence that MSM works to treat inflammatory and immune diseases.

How is MSM given?

MSM is given by mouth in the form of a powder or capsule. It should be given with food or after a meal to prevent stomach upset.

What if I miss giving my pet the supplement?

If you miss a dose, give it when you remember, but if it is close to the time for the next dose, skip the dose you missed and give it at the next scheduled time, and return to the regular dosing schedule. Never give your pet two doses at once or give extra doses.

Are there any potential side effects?

Studies are limited for this supplement and therefore information regarding side effects is also limited. Possible side effects may include stomach upset, diarrhea, decreased appetite, tiredness, restlessness, and headache.

Are there any risk factors for this supplement?

Studies are limited for this supplement and therefore information regarding risk factors is also limited. Do not use MSM in pets that are allergic to it or that are pregnant or nursing, as safety has not been established.

Are there any drug interactions I should be aware of?

The following medications should be used with caution when given with MSM: anticoagulants or nonsteroidal anti-inflammatories (NSAIDs).

Vitamins, herbal therapies, and supplements have the potential to interact with each other, as well as with prescription and over the counter medications. It is important to tell your veterinarian about any medications (including all vitamins, supplements, or herbal therapies) that your pet is taking.

Is there any monitoring that needs to be done with this supplement?

There is no specific monitoring that needs to be done while your pet is taking this medication. Your veterinarian may monitor your pet to be sure that the medication is working.

How do I store MSM?

In general, this supplement should be stored at a cool room temperature, protected from moisture and light. There are many formulations and manufacturers of MSM, so always follow the specific storage instructions on the product label.

What should I do in case of emergency?

If you suspect an overdose or an adverse reaction to the medication, call your veterinary office immediately. If they are not available, follow their directions in contacting an emergency facility.

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