MSM (methylsulfonylmethane) is generally safe for most adults. The FDA has reviewed it and raised no objections to its use in foods, and clinical trials have tested doses up to 6 grams per day for 12 weeks without serious adverse effects. That said, there are some gaps in the safety data, particularly around long-term use and interactions with certain medications, that are worth understanding before you start taking it.
What MSM Is and Why People Take It
MSM is a naturally occurring sulfur compound found in small amounts in foods like fruits, vegetables, grains, and milk. As a supplement, it’s most commonly used for joint pain, particularly osteoarthritis of the knee. It’s also marketed for inflammation, exercise recovery, and skin health. The sulfur it provides plays a role in building connective tissue, which is why it’s often paired with glucosamine in joint health products.
FDA Status
The FDA accepted MSM as “Generally Recognized as Safe” (GRAS) for use as a food ingredient. Specifically, the agency reviewed a notification from Bergstrom Nutrition and stated it had “no questions” regarding the conclusion that MSM is GRAS for use in meal supplements, meal replacement foods, fruit smoothie drinks, thirst quencher beverages (at levels up to 4,000 mg/kg), and food bars like granola and energy bars (at levels up to 30,000 mg/kg). This designation applies to MSM as a food ingredient, not as a therapeutic supplement, but it does indicate that the compound itself has a favorable basic safety profile.
Typical Doses Tested in Studies
Most clinical trials have used doses between 1.5 and 6 grams per day. The National Capital Poison Center notes that suggested doses range from 4 to 6 grams daily, though doses up to 20 grams per day have been used without reports of serious toxicity.
In osteoarthritis studies, common dosing has ranged from 1.5 grams to 6 grams per day, typically split into two or three doses. A study using 6 grams daily for 12 weeks found a 25% reduction in knee pain scores. Another using about 3.4 grams daily for 12 weeks found more modest improvements. These trials reported no significant safety concerns at those doses over the study period.
Common Side Effects
The side effects associated with MSM are mild and digestive in nature. Cleveland Clinic lists the most common ones as constipation, diarrhea, and upset stomach. These typically don’t require medical attention and tend to resolve on their own or with a dose adjustment. Most people tolerate MSM without any noticeable side effects at standard doses.
The Long-term Safety Gap
Here’s the most important caveat: no human study has tracked MSM use beyond 12 weeks. Every major clinical trial has lasted three months or shorter. Since people often take MSM for chronic conditions like osteoarthritis, this is a meaningful gap. An FDA advisory committee presentation noted this directly, stating that “there are no safety data to indicate whether risk increases over time” and that “the lack of long-term safety data for MSM makes it difficult to reliably compare the safety of MSM relative to approved therapies.”
This doesn’t mean long-term use is dangerous. It means it hasn’t been formally studied in a controlled setting, so the risk profile beyond 12 weeks is based on anecdotal and observational evidence rather than clinical trial data.
Potential Interaction With Blood Thinners
One safety signal worth noting involves blood-thinning medications, particularly warfarin. The FDA’s adverse event reporting system and published literature both suggest a possible interaction between MSM and anticoagulant drugs that could increase bleeding risk. The same FDA advisory committee review flagged this as a concern “even with relatively short-term exposure.” If you take warfarin or another blood thinner, this is something to discuss with your prescriber before adding MSM.
There has also been a signal in the literature for elevated blood pressure, though this is less well documented than the anticoagulant concern.
Liver and Kidney Safety
Animal research has actually shown MSM reducing markers of liver stress rather than causing harm. In mice with fatty liver disease, MSM supplementation lowered levels of liver enzymes that indicate damage. However, these are mouse studies, and the researchers themselves cautioned that “it is unclear whether the same results would be observed in humans.” No human clinical trials have reported liver or kidney toxicity from MSM at standard doses, but dedicated organ-function studies in humans are limited.
MSM and Sulfa Allergies
A common concern is whether people with sulfa drug allergies should avoid MSM. MSM contains sulfur, but it is chemically distinct from sulfonamide antibiotics, which are the drugs that cause “sulfa allergies.” Sulfur is an essential element present in many foods and in your body’s own proteins. Having a sulfa drug allergy does not mean you’re allergic to all sulfur-containing compounds. That said, if you have a known sulfa allergy and feel uncertain, starting with a small dose to check for any reaction is a reasonable approach.
Who Should Be Cautious
For most healthy adults taking standard doses of 3 to 6 grams per day, MSM has a reassuring safety profile based on the available evidence. The groups who should exercise more caution include people taking anticoagulant or antiplatelet medications, those with a history of high blood pressure, and anyone with liver or kidney conditions where extra caution with any supplement is warranted. Pregnant and breastfeeding women lack specific safety data for MSM, so the usual guidance of avoiding supplements without clear evidence of safety applies.