What Pain Studies Actually Tell Us About Topical DMSO

The short answer: DMSO alone is not a proven general pain treatment

Current evidence does not establish topical DMSO alone as an effective treatment for pain in general. That includes broad claims about arthritis, sore muscles, chronic pain, nerve pain and injuries. Evidence differs by condition, and a result from one formulation or painful disorder cannot simply be applied to another.

DMSO stands for dimethyl sulfoxide. It is a sulfur-containing solvent associated with wood-pulp processing and papermaking, and it is readily absorbed through intact skin. Its penetration helps explain both the medical interest in DMSO and some of its risks: it can increase the absorption of other substances present in a formulation or on the skin, according to a medically reviewed overview of DMSO’s uses and risks.

Three separate ideas are often blurred together:

1. DMSO has been investigated as a pain treatment.
2. DMSO can help carry certain substances through the skin.
3. DMSO itself has been proved to relieve pain.

The first two statements do not establish the third. A substance can be biologically interesting or useful as a pharmaceutical vehicle without being an effective analgesic on its own.

That distinction matters because some favorable studies concern formulations containing both DMSO and diclofenac, an active pain medicine. If that combination reduces pain, the result does not automatically mean DMSO was responsible. To evaluate DMSO itself, researchers need an appropriate comparison group receiving the DMSO vehicle without diclofenac.

The most informative direct comparison comes from a large knee-osteoarthritis trial. In that study, the DMSO-only vehicle was not significantly more effective than placebo on the measured efficacy outcomes. The diclofenac-containing formulation did better than both, pointing to diclofenac—not standalone DMSO—as the principal therapeutic ingredient in that product.

Biological plausibility, historical popularity, athlete testimonials and personal success stories do not replace controlled comparisons. A placebo-controlled trial is designed to separate those influences from a treatment-specific effect.

Even the negative knee result should not be overgeneralized. It does not prove that DMSO is ineffective for every possible painful condition, concentration, route or duration. It does mean that claims about “DMSO for pain” must be evaluated narrowly:

• What condition was treated?
• Was DMSO used alone or as a vehicle for another drug?
• Was it applied to the skin or administered by another route?
• What was the comparison treatment?
• How long did the study last?
• Were participants and investigators successfully blinded?
• Was the difference large enough to matter in daily life?

On those questions, the overall picture remains uncertain or unfavorable for DMSO alone. Evidence is strongest where DMSO serves as a drug-delivery vehicle, not where it is promoted as a general-purpose topical analgesic.

FDA approval does not include topical treatment of arthritis or general pain

DMSO does have an FDA-approved prescription use, but the route and condition define that approval. The supplied medical sources identify the approved indication as intravesical treatment of interstitial cystitis—a prescription preparation placed inside the bladder under medical supervision. A peer-reviewed review abstract indexed by PubMed describes interstitial cystitis as DMSO’s FDA-approved indication while characterizing pain and osteoarthritis applications as outside that indication.

That use is fundamentally different from buying a DMSO cream, gel or solvent and applying it to a knee, shoulder or muscle. The exposed tissue, formulation, concentration, route, dose, supervision and intended condition are different.

The supplied sources do not identify topical DMSO alone as FDA-approved for arthritis, muscle pain or general chronic pain. Approval for administration inside the bladder does not validate topical use, just as evidence for one disease does not establish effectiveness for another.

Approval status and clinical effectiveness are related but separate questions. Lack of approval does not prove that every off-label use is ineffective. It means that the particular product, route and indication have not received approval for marketing on that basis; the clinical evidence must still be evaluated directly.

Three uses that should not be confused

Category	What it involves	What can be concluded
Approved intravesical use	Prescription DMSO administered inside the bladder for interstitial cystitis	Supports a specific medically supervised route and indication—not topical pain treatment
DMSO-only topical pain use	A cream, gel or liquid applied to a painful joint or muscle	Not identified in the supplied sources as FDA-approved for arthritis, muscle pain or general chronic pain; efficacy remains unestablished
Topical medicine using DMSO as a vehicle	An active drug, such as diclofenac, formulated with DMSO to aid skin delivery	Evidence may support the complete formulation, but it cannot automatically be credited to DMSO alone

This distinction also prevents a common product-comparison error. A retail DMSO-only gel is not equivalent to a defined topical medicine containing diclofenac in a DMSO vehicle. Sharing one ingredient does not make the formulations interchangeable.

What the evidence shows for different kinds of pain

There is no single answer for every kind of pain. The available findings range from a substantial negative comparison in knee osteoarthritis to small, conflicting or incompletely described findings in other conditions.

The confidence descriptions below are editorial summaries, not formal GRADE ratings. They reflect the directness, size and consistency of the evidence available in the supplied sources.

Condition	Formulation or route	Comparator	Main finding	Confidence	Main limitation
Knee osteoarthritis	Topical DMSO vehicle alone	Topical placebo	No significant advantage on measured efficacy outcomes in a 12-week trial of 775 adults (trial report)	Strongest direct evidence available here	Addresses one vehicle, condition and treatment period
Knee osteoarthritis	Diclofenac in 45.5% DMSO	Placebo, vehicle or oral diclofenac	Improved pain, function and patient assessment in several randomized trials (evidence review)	Multiple direct trials for the complete formulation	Diclofenac is an active NSAID, so benefit cannot be assigned to DMSO alone
Osteoarthritis, older preliminary research	Topical DMSO-only preparations	Placebo	Some older reports were positive	Small or methodologically uncertain studies	Results conflict with the larger DMSO-vehicle comparison
Tendinopathy	Topical DMSO gel or solution	Placebo or low-concentration DMSO	Conflicting: one report favored 10% gel, while another found no difference between 70% DMSO and a 5% comparator (health-system summary)	Small, dated and conflicting evidence	Incomplete study details and a comparator that may not have been inert
Complex regional pain syndrome	Topical DMSO	Control varied by study	A secondary medical summary rates it as possibly effective (condition summary)	Secondary-summary evidence only	Insufficient primary-trial detail for a firm recommendation
Shingles-related pain	DMSO combined with idoxuridine	Other regimens	Favorable secondary summaries exist	Combination evidence only	The active antiviral prevents isolation of DMSO’s effect
Rheumatoid arthritis	Topical DMSO	Varied or incompletely described	Preliminary suggestions only	Preliminary evidence	No robust confirmatory evidence in the supplied material
Sprains and strains	Topical DMSO	Not clearly established	No controlled confirmation in the reviewed summary	Historical use rather than dependable trial evidence	The source review is dated and not a systematic search
Back pain, neuropathy, migraine, fibromyalgia, acute injuries or generalized pain	Varied or unspecified	Varied or absent	Benefit is not established by the supplied evidence	No directly applicable evidence presented	Findings from knee arthritis or combination products cannot be extrapolated

Knee osteoarthritis

Older sources describe preliminary positive osteoarthritis studies, including a short trial of a DMSO gel. Small positive studies should not outweigh a larger, better-controlled study without close examination of design.

The more informative knee comparison included both a DMSO-only vehicle arm and a separate topical-placebo arm. DMSO did not significantly outperform placebo. That does not settle every question about every joint or DMSO formulation, but it directly challenges the claim that topical DMSO is an established treatment for knee-osteoarthritis symptoms.

Tendinopathy

The tendinopathy evidence is contradictory. An older health-system summary reports that one double-blind trial favored a 10% DMSO gel for elbow and shoulder tendinopathy, while another found no difference between a 70% solution and a 5% DMSO comparison solution.

DMSO’s recognizable odor can also reveal treatment assignment, weakening blinding when outcomes such as pain are subjective. Without stronger modern replication, these reports do not establish a dependable tendinopathy treatment.

The concentrations are study characteristics, not application recommendations.

Complex regional pain syndrome

One secondary medical reference classifies topical DMSO as possibly effective for pain associated with complex regional pain syndrome. That is a narrower and more tentative conclusion than saying DMSO treats chronic pain generally.

The supplied material does not provide enough current primary-trial detail—such as effect size, risk of bias, replication or durability—to support a firm recommendation. Complex regional pain syndrome is also a serious diagnosis that warrants clinical assessment rather than self-treatment of unexplained burning, swelling, sensitivity or persistent limb pain.

Shingles-related pain

Positive summaries for shingles-related pain concern DMSO combined with idoxuridine, an active antiviral medicine. A combination can work because of the active drug, its delivery, an interaction between ingredients or all three.

Without a suitable DMSO-only comparison, those results cannot show that DMSO itself relieved shingles pain.

Rheumatoid arthritis, sprains and strains

Evidence for rheumatoid arthritis remains preliminary in the supplied material. Even if a topical product reduced symptoms, that would not by itself show that it controls the disease or prevents joint damage.

For sprains and strains, the older summary reports no controlled confirmation. Historical use for sports injuries does not demonstrate faster healing, tissue repair or reliable pain relief.

The supplied evidence likewise does not establish DMSO as a treatment for back pain, peripheral neuropathy, migraine, fibromyalgia, acute injuries or generalized pain. This is a conclusion about the evidence provided here, not a claim that every study ever conducted has been exhaustively excluded. These conditions have different causes, and a study in primary knee osteoarthritis cannot answer whether DMSO helps them.

The key knee-osteoarthritis trial: DMSO vehicle versus placebo

The most useful trial for separating DMSO from a drug carried in DMSO was a 12-week, double-blind, double-dummy randomized trial involving 775 adults with radiologically confirmed symptomatic primary knee osteoarthritis. Its five groups received topical diclofenac in a DMSO vehicle, topical placebo, DMSO vehicle without diclofenac, oral diclofenac, or combined topical and oral diclofenac (published trial).

The double-dummy design meant participants received corresponding topical and oral preparations so that the treatment comparisons could be masked. Even so, DMSO’s characteristic odor and skin effects may make successful blinding difficult.

The decisive comparison for DMSO itself was not topical diclofenac versus placebo. It was DMSO vehicle alone versus topical placebo. The DMSO vehicle was not significantly more effective than placebo on the trial’s efficacy measures.

By contrast, topical diclofenac in the DMSO vehicle improved several outcomes relative to topical placebo and was superior to the DMSO vehicle on all efficacy variables. That pattern supports the role of diclofenac and the complete formulation while providing no evidence from this trial that the DMSO vehicle independently relieved knee-osteoarthritis symptoms.

This illustrates why ingredient-specific controls matter. If a cream contains an established pain medicine plus a penetration-enhancing substance, several explanations are possible when the cream works:

1. The active medicine produced the benefit.
2. The vehicle improved delivery of the active medicine.
3. Both ingredients had independent therapeutic effects.
4. The complete formulation behaved differently from either ingredient alone.

A DMSO-only arm helps distinguish those possibilities. Here, that arm failed to outperform placebo, while diclofenac in the same vehicle did.

The study had important limitations. Of the 775 randomized participants, 527 completed treatment, so approximately one-third did not complete the trial. The manufacturer supplied the medication, funded the study, and managed and analyzed the data. Neither attrition nor commercial funding automatically invalidates a result, but both matter when judging confidence and the need for independent replication.

The findings are also bounded by the population and duration. This was primary knee osteoarthritis treated for 12 weeks. It did not establish outcomes for:

• Osteoarthritis of the hip, hand, shoulder or spine
• Acute sprains, strains or traumatic injuries
• Inflammatory arthritis
• Neuropathic pain
• Back pain
• Fibromyalgia or migraine
• Repeated use beyond the trial period

The sound conclusion is specific: in this trial, the tested DMSO vehicle did not relieve knee-osteoarthritis symptoms better than placebo. That is neither proof that every conceivable DMSO use must fail nor evidence supporting its use for unrelated conditions.

DMSO alone is not the same as diclofenac delivered in DMSO

Diclofenac is a nonsteroidal anti-inflammatory drug, or NSAID. In the relevant combination studies, diclofenac is the active pain medicine and DMSO serves as a penetration-enhancing vehicle.

A review evaluated five double-blind randomized trials of a topical solution containing diclofenac and 45.5% DMSO in adults with radiographically verified primary knee osteoarthritis. The complete formulation improved pain, physical function and patient assessment compared with placebo or vehicle controls. Two studies reported outcomes similar to oral diclofenac, including one reporting statistical equivalence. Trial durations ranged from four to 12 weeks (review of the combination formulation).

Those findings support the formulated medicine. They do not establish that plain DMSO is an analgesic. The large trial’s DMSO-only arm points in the opposite direction for that particular knee-osteoarthritis setting.

What is being tested?	What the study can evaluate	What it cannot establish
DMSO alone versus placebo	Whether that DMSO formulation has an independent treatment effect	Whether an active drug delivered in DMSO works
Diclofenac in DMSO versus placebo or DMSO vehicle	Whether adding diclofenac improves outcomes and whether the complete formulation works	That a DMSO-only retail product provides the same benefit
Diclofenac in DMSO versus diclofenac in another vehicle	Whether the formulations differ in performance	Whether a difference reflects independent DMSO analgesia, enhanced drug delivery or another formulation feature

A separate 12-week trial of 43 adults compared a DMSO-based diclofenac solution with a linseed-oil-based diclofenac gel. The DMSO formulation produced statistically greater changes in pain, stiffness and physical function. However, both groups received diclofenac, and there was no DMSO-only arm (small randomized formulation trial).

A statistically significant difference is not automatically a clinically meaningful one. Statistical significance concerns how compatible a result is with a no-difference model under specified assumptions. Clinical importance asks whether the improvement is large enough for patients to notice or value. The small trial’s abstract reported statistically significant differences but did not establish whether they crossed a recognized threshold for meaningful improvement.

Its size also limits safety conclusions. A 12-week study involving 43 participants cannot reliably detect uncommon adverse effects or establish long-term safety, even when no adverse events are reported.

Across the combination-product evidence supplied here, follow-up lasted no longer than 12 weeks. That permits assessment of short-term symptom changes but not cumulative exposure, uncommon harms or sustained effectiveness over years of chronic osteoarthritis.

For shoppers, the practical question is not simply, “Does this contain DMSO?” It is, “What is the active ingredient, and what exact formulation was tested?” A DMSO-only retail gel should not borrow evidence from a diclofenac-containing formulation.

Skin penetration is both DMSO’s proposed advantage and its central risk

DMSO rapidly penetrates intact skin and can facilitate delivery of other compounds. That may make it useful as a pharmaceutical vehicle when a medicine is deliberately formulated and evaluated around that property.

The same characteristic creates uncertainty outside a controlled formulation. DMSO may increase exposure not only to an intended medicine but also to other substances on the skin or mixed into a product. Medically reviewed guidance warns that it can carry substances through the skin and may increase the effects of medicines (DMSO safety overview).

• Residue from another topical medication
• Pain creams, steroid creams or anesthetic products
• Cosmetics, fragrances, lotions and sunscreen
• Dirt, cleaning chemicals or occupational residues
• Garden or agricultural pesticides
• Impurities introduced during manufacturing, storage or handling

This does not mean every substance on the skin will be absorbed equally or cause harm. The amount and clinical significance depend on the substance, formulation and circumstances. The concern is that exposure becomes harder to predict, especially when products are layered or the DMSO source is poorly characterized.

Purity and efficacy answer different questions. Cleaner material may reduce the risk of transporting manufacturing contaminants through the skin. It does not demonstrate that DMSO relieves pain. “High purity” is a chemical-quality claim, not a clinical efficacy result.

Industrial, veterinary, solvent-grade or otherwise poorly sourced material should not be treated as interchangeable with a medically evaluated formulation. Because DMSO facilitates skin penetration, unknown impurities are especially concerning.

A high concentration on a label does not establish greater effectiveness. Nor does a pharmaceutical-sounding label prove that a retail product was manufactured, tested or regulated like an approved medicine.

Applying several topical products to the same area creates further uncertainty. A clinician or pharmacist should review prescription creams, over-the-counter pain products, cosmetics and other topical preparations before they are combined with DMSO.

DMSO’s penetration is therefore a double-edged property. It may be valuable in a carefully designed medicine, but in unsupervised use it also makes contamination, interaction and dosing questions harder—not easier.

Side effects, medication concerns and people who should not self-treat

The reported safety profile varies by route, concentration, formulation, dose and duration. The supplied evidence does not provide a complete safety profile for repeated, unsupervised topical use, especially over the long term.

Application-site effects

Reported effects after topical exposure include irritation, dryness, itching, burning, rash, scaling, blistering and changes in skin pigmentation. Skin reactions were more associated with topical use in a medically reviewed summary of human adverse-effect reports (review of DMSO for arthritis and safety).

Dryness was particularly common in trials of diclofenac formulated with DMSO, although that observation applies to the complete combination product rather than DMSO alone. Improperly prepared or poorly characterized products may create additional irritation or contamination concerns.

Odor and taste effects

DMSO metabolism can produce a distinctive garlic-like breath, taste or body odor. This is more than a social inconvenience in research: a recognizable odor may reveal who received DMSO, weakening blinding in trials that rely on subjective pain ratings.

Neurological and general symptoms

Headache, dizziness and drowsiness have been reported. Some references also list light sensitivity or visual symptoms, although the evidence and relevance vary by route and exposure. These reports are reasons not to assume that applying a substance to the skin necessarily limits all effects to the application site.

Gastrointestinal symptoms

Reported gastrointestinal effects include nausea, vomiting, diarrhea and abdominal discomfort. Their frequency and relevance may differ between topical, oral, intravenous and intravesical exposure.

Warning signs requiring medical help

These warning signs appear in secondary medical summaries of reported DMSO adverse effects (precautions and adverse-effect summary).

Do not respond to a serious reaction by applying more DMSO, adding another topical product or attempting an improvised neutralizing treatment. The appropriate level of care depends on the symptoms and exposure.

Medication and topical-product concerns

The evidence does not provide a definitive interaction list. An older summary reported no known interactions at the time of its review while acknowledging that unknown interactions could exist. More recent consumer references warn that DMSO’s effect on absorption may increase the effects or adverse effects of medicines.

One medically reviewed source specifically cautions about blood thinners, steroids and sedatives. The broader concern also applies to other medicines and topical products because DMSO may alter absorption. That does not prove a clinically important interaction with every drug, but it makes a blanket “no interactions” claim unjustified.

Ask a clinician or pharmacist to review DMSO before use if you:

• Take several prescription or over-the-counter medicines
• Use anticoagulant or antiplatelet medicines
• Take sedating medication
• Use oral, injected or topical steroids
• Apply prescription creams, gels or patches to the same area
• Have previously reacted to topical medicines or solvents

Do not assume that separating two topical products by a few minutes eliminates the concern. The supplied evidence does not establish a general spacing rule that makes an unapproved DMSO product compatible with every topical medicine.

People who should avoid self-treatment

Pregnancy and breastfeeding are reasons to avoid self-treatment because reliable safety information is lacking. People with diabetes, asthma, certain blood disorders, or liver or kidney disease should also seek individualized medical advice before considering DMSO. These precautions reflect unresolved safety, metabolism and interaction questions rather than proof that every person in one of these groups will be harmed.

The supplied evidence also does not establish oral, intravenous or other unsupervised routes as safe or effective for pain. A product sold for topical use should never be assumed suitable for swallowing, injection or infusion.

How to make a safer evidence-based decision without a home DMSO protocol

The research does not establish a validated home dose, dilution, application frequency or treatment duration for DMSO alone. Studies have used different formulations and schedules for different conditions, sometimes under medical supervision. Turning one research method into general instructions would ignore differences in diagnosis, product quality, route, monitoring and comparator.

Retail products may be sold in widely varying concentrations, but that range is not an evidence-based dose ladder. A stronger product is not necessarily more effective or safer. Concentration alone says little about manufacturing quality, formulation behavior or suitability for a particular person.

Before considering DMSO for pain, discuss the following with a clinician or pharmacist:

• The location, cause and duration of the pain. Joint pain can reflect osteoarthritis, inflammatory arthritis, gout, infection, injury or referred pain.
• Whether there is a diagnosis. Evidence from primary knee osteoarthritis does not automatically apply to undiagnosed back, hip, shoulder or nerve pain.
• Current oral medicines. Include prescriptions, over-the-counter pain relievers, sleep products and supplements.
• Current topical products. Include prescription creams, patches, cosmetics, lotions and products used only occasionally.
• Pregnancy or breastfeeding status.
• Relevant medical conditions. Mention diabetes, asthma, blood disorders, liver disease, kidney disease, allergies and previous skin reactions.
• The proposed product source and intended use. A vague “high purity” claim does not answer how the product was manufactured, tested or regulated.
• Whether the product contains DMSO alone or an active medicine in DMSO. The benefit evidence and medication risks differ.
• Evidence-based alternatives for the diagnosed condition. The relevant choice is not necessarily DMSO versus doing nothing.

Persistent, severe, unexplained or worsening pain deserves clinical evaluation rather than assumptions based on a knee-osteoarthritis study.

When reviewing a DMSO claim, consider the study features that affect confidence:

• Condition specificity: Was the trial conducted in people with the same diagnosis?
• Formulation: Was DMSO tested alone or with an active medicine?
• Comparator: Was it compared with an inert placebo, low-concentration DMSO or another active treatment?
• Blinding: Could odor or skin effects reveal treatment assignment?
• Sample size: Was the study large enough to provide a stable estimate?
• Follow-up: Did it last long enough to address chronic use?
• Attrition: How many randomized participants failed to complete treatment?
• Reporting: Were allocation methods, outcomes and adverse effects fully described?
• Funding: Who supplied the product, managed the data and analyzed the results?
• Clinical importance: Was the difference meaningful to patients, or only statistically significant?

These are not technical excuses for dismissing positive results. They determine how much confidence a result deserves. The small diclofenac-formulation trial, for example, reported statistically favorable outcomes but provided limited methodological detail in its abstract and did not include a DMSO-only group.

Testimonials cannot resolve these limitations. Neither can historical popularity or claims that regulators suppressed a cure. A McGill University critical review of DMSO’s evidence and history discusses weak controls, blinding difficulties, impurity concerns and the lack of robust long-term safety research.

The decision comes down to three separate judgments:

1. Benefit: The evidence does not establish DMSO alone as a general pain treatment, and the strongest direct knee-osteoarthritis comparison found no advantage over placebo.
2. Short-term risk: Skin reactions, systemic symptoms, altered absorption and contamination are identifiable concerns.
3. Long-term risk: Repeated-use safety remains unresolved because the represented studies are condition-specific and generally short.

DMSO’s ability to penetrate skin may make it useful as a carefully controlled drug-delivery vehicle. That property is not proof that DMSO relieves pain, and it creates unusual absorption and contamination risks. Favorable findings for diclofenac-in-DMSO formulations mainly support diclofenac and the complete formulation—not DMSO-only retail products.

With no validated home regimen and no robust long-term safety record, the safer approach is to obtain a diagnosis and request clinician or pharmacist review rather than extrapolate from testimonials, retail concentrations or studies of unrelated formulations.

Does DMSO work better than placebo for osteoarthritis pain?

Not in the strongest direct DMSO-only comparison reviewed here. In the large 12-week knee-osteoarthritis trial, the DMSO vehicle was not significantly more effective than placebo on the measured efficacy outcomes.

Some older, smaller studies were reported as positive. The appropriate conclusion is therefore specific: the evidence does not establish DMSO alone as an effective osteoarthritis treatment, and the best direct knee comparison was negative. That does not prove every possible formulation will produce identical results in every joint.

Is topical DMSO FDA-approved for arthritis, muscle pain or chronic pain?

No such topical approval is identified in the supplied sources. They describe DMSO’s FDA-approved prescription indication as intravesical treatment of interstitial cystitis—not topical treatment of arthritis, muscle pain or general chronic pain (approval summary).

Approval of one route and condition does not extend to retail creams, gels or solvents. A medically supervised bladder treatment and a topical consumer product are not interchangeable.

Does diclofenac in DMSO prove that DMSO itself relieves pain?

No. Diclofenac is an active NSAID, while DMSO acts as a skin-penetrating vehicle in the reviewed formulations. Trials showing that diclofenac in DMSO improves knee-osteoarthritis symptoms support the complete drug formulation.

The most informative large trial included a DMSO-only arm, which did not outperform placebo. Smaller comparisons in which both groups received diclofenac can assess formulation differences but cannot isolate an analgesic effect of DMSO. That limitation also applies to the 43-person diclofenac-formulation study described above (trial abstract).

Can DMSO carry medicines, cosmetics or contaminants through the skin?

DMSO readily penetrates skin and can facilitate the absorption of other substances. Those may include intended medicines as well as topical-drug residue, cosmetics, lotions or product impurities.

The amount absorbed depends on the substance and circumstances, so this is not a claim that everything touching DMSO enters the body equally. It is a reason to avoid combining products without professional review and not to treat industrial, veterinary or poorly sourced material as suitable for medical use.

Is there a proven DMSO concentration or application schedule for pain?

No validated home concentration, dilution, dose, frequency or treatment duration is established by the evidence reviewed here. Research has used differing concentrations and schedules for different conditions and formulations, sometimes under medical supervision.

Those study methods should not be converted into home instructions. A higher retail concentration does not prove greater effectiveness or safety, and greater purity may reduce one contamination concern without demonstrating pain relief.