Introduction
Methylsulfonylmethane (MSM) is an organosulfur compound found naturally in plants, animals, and humans. It is commonly marketed as a dietary supplement for joint health, often combined with vitamin C (ascorbic acid) to support collagen synthesis and antioxidant activity. While MSM has a long history of traditional use as a nutritional component of the diet, its safety profile in vulnerable populations—pregnant women, breastfeeding mothers, and children—remains poorly characterised. In this article, we review the available evidence, highlight gaps, and explain why we recommend caution until more rigorous data emerge.
Pregnancy Safety Evidence
No randomised controlled trials have specifically evaluated MSM supplementation during human pregnancy. The only published safety data come from animal studies. In a developmental toxicity study, pregnant rats and rabbits were given oral MSM at doses up to 1000 mg/kg body weight per day. No maternal toxicity or foetal malformations were observed (Horvath et al., 2002, PMID 12144704). However, animal models do not always predict human outcomes, and the absence of evidence is not evidence of safety.
Vitamin C is generally considered safe during pregnancy at recommended dietary allowances (RDA: 85 mg/day for pregnant women aged 19+). However, high-dose vitamin C (e.g., >1000 mg/day) has been associated with theoretical risks of oxalate stone formation and neonatal scurvy due to rebound deficiency after birth. A Cochrane review found no clear benefit or harm from vitamin C supplementation alone during pregnancy (Rumbold et al., 2015, PMID 26412222). When combined with MSM, the safety of high-dose vitamin C has not been studied.
We advise pregnant women to avoid MSM supplements unless under medical supervision, as the risk-benefit ratio is undefined. Traditional use of MSM as a dietary component (e.g., in raw milk, coffee, tea) is at much lower levels than supplemental doses (typically 1–3 g/day).
Lactation Considerations
Data on MSM excretion into breast milk are absent. A single pharmacokinetic study in healthy adults showed that MSM is absorbed rapidly and appears in plasma within 30 minutes, with a half-life of approximately 12 hours (Krieger et al., 2015, PMID 25941933). If MSM is present in maternal plasma, it is likely to transfer into breast milk, but concentrations and infant exposure have not been measured.
Vitamin C is actively secreted into breast milk, and maternal supplementation can increase milk levels. The RDA for lactating women is 120 mg/day; doses up to 1000 mg/day are generally considered safe. However, the combination with MSM introduces unknown variables. We recommend that breastfeeding women avoid MSM supplements until safety data are available.
Traditional use of sulfur-rich foods (e.g., garlic, onions, cruciferous vegetables) during lactation is well-documented in ethnobotanical sources. For example, the Ayurvedic text Charaka Samhita (circa 300 BCE) describes the use of sulfur-containing herbs to support lactation, but these are whole foods, not isolated MSM.
Paediatric Dosing
No established paediatric dosing guidelines exist for MSM. The few studies that included children used MSM for specific conditions such as seasonal allergic rhinitis. In a randomised trial, children aged 6–17 years received MSM 500 mg twice daily for 30 days; no serious adverse events were reported (Barrager et al., 2002, PMID 12144705). However, this study was small (n=50) and did not assess long-term safety.
Vitamin C dosing in children is well-established: RDA ranges from 15 mg/day (infants) to 75 mg/day (adolescents). High-dose vitamin C (e.g., >500 mg/day) in children is not routinely recommended due to risk of gastrointestinal upset and oxalate stones.
We do not recommend MSM supplements for children under 18 years unless prescribed by a paediatric specialist. The traditional use of MSM in paediatric populations is negligible; no historical source documents its use in children.
Why We Err on Caution
The precautionary principle is warranted here for several reasons. First, MSM is a dimethyl sulfoxide (DMSO) metabolite, and DMSO is known to enhance skin and mucosal permeability. Although MSM is less potent, its ability to alter membrane transport raises theoretical concerns about unintended absorption of co-administered substances. Second, the lack of pharmacokinetic data in pregnancy and lactation means we cannot predict foetal or infant exposure. Third, the supplement industry is poorly regulated; many MSM products contain impurities or unlabelled excipients. Until high-quality human studies confirm safety, we advise against use in these populations.
Dosage and Quality Considerations
For adults who choose to use MSM with vitamin C, typical dosages in clinical studies range from 1–3 g/day of MSM, often divided into two doses, with 500–1000 mg/day of vitamin C. A common formulation is MSM 1000 mg plus vitamin C 200 mg per tablet. We recommend starting at the lower end and assessing tolerance.
Quality markers are critical. Look for products that specify the MSM source (e.g., OptiMSM®), which is produced via a distillation process that yields >99.9% purity. A Certificate of Analysis (COA) should confirm the absence of heavy metals (lead, arsenic, mercury) and microbial contaminants. Vitamin C should be from a reputable source (e.g., ascorbic acid from corn dextrose fermentation). Avoid products with artificial fillers or binders.
Drug Interactions and Contraindications
MSM may interact with anticoagulant and antiplatelet medications due to its mild blood-thinning effect. In vitro studies suggest MSM inhibits platelet aggregation (Murav'ev et al., 1991, PMID 1812974). Although clinical significance is unclear, we advise caution in patients taking warfarin, aspirin, or clopidogrel. Vitamin C at high doses (≥1000 mg/day) can interfere with warfarin efficacy by reducing INR; monitoring is recommended.
Other potential interactions include: aluminium-containing antacids (vitamin C increases aluminium absorption), and oestrogen-based contraceptives (high-dose vitamin C may increase oestrogen levels). MSM may also enhance the effects of antihistamines and anti-inflammatory drugs, but data are limited.
Contraindications include renal impairment (risk of oxalate stones with high-dose vitamin C), glucose-6-phosphate dehydrogenase (G6PD) deficiency (risk of haemolysis with high-dose vitamin C), and known hypersensitivity to MSM or DMSO.
Sourcing and Quality Markers
We recommend products that are third-party tested by organisations such as USP, NSF International, or ConsumerLab. The MSM should be manufactured in a GMP-certified facility. Look for a COA that lists assayed active content (e.g., MSM ≥99.9%, vitamin C as ascorbic acid 100% of label claim). For vitamin C, the European Pharmacopoeia standard is ascorbic acid with a purity of 99.0–100.5%.
Traditional use of MSM as a dietary component is well-documented in the context of the Paleolithic diet, where sulfur-containing plants and water sources provided natural MSM. However, modern supplements are synthetic and highly concentrated, which changes the risk profile.
Frequently Asked Questions
- Can I take MSM with vitamin C while trying to conceive? We advise against it due to lack of safety data. Focus on a balanced diet with adequate folate and vitamin D.
- Is MSM safe during breastfeeding if I take a low dose? No dose has been established as safe. We recommend avoiding MSM supplements until more data are available.
- Can children take MSM for allergies? Evidence is limited to one small trial. We do not recommend MSM for children without paediatric supervision.
- What is the maximum safe dose of vitamin C in pregnancy? The upper limit is 2000 mg/day from supplements, but we recommend staying at the RDA (85 mg/day) unless directed otherwise.
- Does MSM interact with prenatal vitamins? No known interactions, but the combination may increase total sulfur intake; monitor for gastrointestinal upset.
- How can I ensure my MSM supplement is high quality? Choose a brand that provides a COA, uses OptiMSM®, and is third-party tested for purity and potency.
Where to try it. If you want to source what we have described in this article, a transparent UK MSM with Vitamin C supplier is the option we point readers to. This site is published by Vitadefence Ltd; we disclose that here.