Drug & supplement interaction

Dimethylsulfoxide (dmso) + Fluorouracil

Fluorouracil brand names: Efudex, Tolak.

Moderate Interaction
Medically reviewed by · Updated September 2026
The bottom line Moderate

Dimethylsulfoxide (dmso) has a moderate interaction with Fluorouracil. Topical DMSO might increase the effects and adverse effects of topical drugs.

Read the full interaction report
SeverityModerate
LikelihoodPossible
EvidenceB
What do Severity, Likelihood & Evidence mean?
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Interaction report

Dimethylsulfoxide (dmso) and Fluorouracil

Here is the interaction we found between these two, with the evidence behind it.

Moderate

TOPICAL DRUGS

Why this applies to Fluorouracil

Fluorouracil falls under TOPICAL DRUGS — the group Dimethylsulfoxide (dmso) interacts with.

Topical DMSO might increase the effects and adverse effects of topical drugs.
Evidence from animal studies and limited human studies suggests that DMSO may potentiate the action of numerous topical medications by increasing their absorption through the skin. This increase in absorption seems to depend on the concentration of DMSO and the molecular weight of the medication.
Severity Moderate Likelihood Possible Evidence B

Interaction has been documented in animal or in lab research, or the interaction has been documented in humans but is limited to case reports or conflicting clinical research exists.

Dr. Brian Staiger, PharmD, BCPS
Dr. Brian Staiger explains PharmD, Clinical Pharmacist

The form of fluorouracil that matters here is the skin cream (brands like Efudex and Tolak), which you dab onto spots such as actinic keratoses. DMSO's main trick is that it helps other substances slip through the skin more easily. So if you put DMSO on the same area, it could drive more of your fluorouracil cream into the skin than intended.

With this drug, that usually means a stronger local reaction: more redness, burning, stinging, crusting, peeling, or soreness where you applied it. This is based on animal work and limited human data, so it's a reasonable concern rather than a certainty. Please don't layer DMSO over your fluorouracil, and check with your pharmacist or doctor before using DMSO anywhere on your skin.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Jacob SW, Herschler R. Pharmacology of DMSO. Cryobiology 1986;23:14-27. PubMed
  2. Capriotti K, Capriotti JA. Dimethyl sulfoxide: history, chemistry, and clinical utility in dermatology. J Clin Aesthet Dermatol. 2012;5(9):24-6.
  3. DOMOSO SOLUTION (90% Dimethyl Sulfoxide). Fort Dodge Animal Health, Fort Dodge, Iowa. Avaliable at: https://www.zoetisus.com/_locale-assets/mcm-portal-assets/products/pdf/domoso_solution_pi.pdf. Accessed 8/3/2020.

What These Ratings Mean

Every interaction above is graded three ways — here’s the key to each label.

Severity how clinically significant the interaction is
Major

Clinically significant. Avoid the combination, or use only under close professional supervision.

Moderate

Usually worth avoiding or managing — may need monitoring, a dose change, or timing apart.

Minor

Generally not serious. Be aware of it and mention it to your pharmacist.

Likelihood how strong the evidence is that the interaction actually happens in people
  • LikelyWell-controlled human studies have demonstrated the likely existence of this interaction.
  • ProbableInteraction has not been documented in well-controlled studies, however, the interaction has been demonstrated in some small human studies or in controlled animal studies in conjunction with multiple case reports.
  • PossibleInteraction has been documented in animal or in lab research, or the interaction has been documented in humans but is limited to case reports or conflicting clinical research exists.
  • UnlikelyInteraction has been demonstrated in animal or in lab research but has been shown not to occur in humans.
Evidence the quality of the studies behind the rating (graded A–D)
  • AHigh-quality meta-analysis (quantitative systematic review).
  • BCase-control study.
  • CConsensus.
  • DAnecdotal evidence.

These ratings are for information only. Never start, stop, or otherwise change your therapy before speaking with your provider.

Keep it in perspective

Dimethylsulfoxide (dmso) Also Interacts With Other Medications

Dimethylsulfoxide (dmso) has 338 moderate known drug interactions in our database — the Fluorouracil one above is one of them. If you take anything else, check it against the full list below.

Moderate 338 No known interaction 2,492 (incl. Fluorouracil)
Taking anything else?

Check Another of Your Medications Against Dimethylsulfoxide (dmso)

Covers the 2,830 medications we’ve checked against Dimethylsulfoxide (dmso). Pick one to open its full report.

Everything else you take

See Every Supplement That Interacts With Fluorouracil

This page covers Dimethylsulfoxide (dmso) only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Fluorouracil page lists 26 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: Alfalfa (moderate), Angelica Archangelica (moderate), Arrach (moderate), Bergamot (moderate) and Bishop's Weed (moderate).

By severity: 23 moderate · 3 minor.

From our pharmacist’s overview on the Fluorouracil page

“If you are using fluorouracil cream (Efudex, Tolak) on sun-damaged skin, your skin is already primed to react to sunlight, and that is where most of its supplement interactions sit. Of the 26 ingredients on file, 20 can make skin more sun-sensitive on their own, chlorophyll, chlorella, and bergamot oil among them, so pairing one with t…”

Reviewed by 2 · Jul 18, 2026

Open the Fluorouracil interaction page

How much people look this up

Where Dimethylsulfoxide (dmso) and Fluorouracil Sit Against Everything Else

Out of every supplement and medication people look up on HelloPharmacist, here is where these two land this week — and which way each has been moving.

Supplement Dimethylsulfoxide (dmso)
Top half

#649 of 1,452 supplements looked up here in the last 7 days

29 days ago today
Medication Fluorouracil
Steady interest

#2,357 of 2,830 medications looked up here in the last 7 days

29 days ago today

Position among everything looked up on this site, not a measure of how commonly either one is used or how important it is. A supplement can climb this list because of a news story. It counts every request to the page, automated ones included, and nothing here identifies anyone.

Supplement

About Dimethylsulfoxide (dmso)

What is Dimethylsulfoxide (dmso)?

Dimethylsulfoxide (dmso)
  • Muscle and joint pain
  • Arthritis
  • Sprains and strains
  • Interstitial cystitis (bladder pain)
  • Skin penetration enhancer for other medicines

DMSO is a colorless liquid solvent that people apply to the skin for pain and inflammation, and it is FDA-approved (as a prescription) only for interstitial cystitis placed directly into the bladder. Most over-the-counter uses for pain and arthritis have limited or low-quality evidence, and DMSO can carry impurities or push other chemicals through your skin. Talk to your pharmacist or doctor before using it, and avoid industrial-grade products.

Read the full Dimethylsulfoxide (dmso) monograph & all interactions
Medication

About Fluorouracil Injection

What Is Fluorouracil Injection Used For?

Brand names: Efudex, Tolak

Fluorouracil Injection is used to treat four types of adenocarcinoma (a common form of cancer that begins in glandular cells): cancer of the colon and rectum, breast cancer, stomach (gastric) cancer, and pancreatic cancer.

It is nearly always given as part of a combination chemotherapy regimen alongside other cancer medicines, and the specific drugs paired with it depend on which cancer is being treated.

See full Fluorouracil Injection drug information
Keep checking

Other Drugs & Dimethylsulfoxide (dmso)

Browse every other medication we’ve checked against Dimethylsulfoxide (dmso) — both the ones with a known interaction and the ones without. Select any drug for the full detail.

0Major
338Moderate
0Minor
2,491No known interaction
338 Moderate 2,491 No interaction
Moderate

338 interactions

Showing 60 of 338 moderate interactions — see all 338 on the Dimethylsulfoxide (dmso) page.

No interaction 2,491 drugs checked — show the list

We also checked Dimethylsulfoxide (dmso) against these medications and found no known interaction in our sources. Open any page to confirm.

Showing the 60 most looked-up of 2,491 medications checked with no known interaction — see the full Dimethylsulfoxide (dmso) list.

See the full Dimethylsulfoxide (dmso) interactions page
See every supplement checked against Fluorouracil, ranked by severity
Sources

Sources & How We Checked

Interaction details are evidence-graded and sourced from the Natural Medicines database. The medication overview comes from MedlinePlus.

Content is written and reviewed by licensed HelloPharmacist pharmacists. See our data sources and editorial standards for how this information is built and checked.

Parts of this content are provided by the Therapeutic Research Center, LLC.

DISCLAIMER: Currently this does not check for drug-drug interactions. This is not an all-inclusive comprehensive list of potential interactions and is for informational purposes only. Not all interactions are known or well-reported in the scientific literature, and new interactions are continually being reported. Input is needed from a qualified healthcare provider including a pharmacist before starting any therapy. Application of clinical judgment is necessary.

© 2021 Therapeutic Research Center, LLC

Keep exploring
Dimethylsulfoxide (dmso) monograph › Uses, safety, and every drug interaction in one place Fluorouracil supplement interactions › Every supplement checked against Fluorouracil, ranked by severity Fluorouracil Injection drug information › The full plain-English guide to this medication Supplement interaction checker › Check any supplement or product against your medications Browse medications A–Z › Every drug we've checked against herbs & supplements Ask a pharmacist › Free, personal answer from our licensed team
Pharmacist Counseling Corner

Taking Dimethylsulfoxide (dmso) and Fluorouracil Together: Common Questions

Can you take Dimethylsulfoxide (dmso) with Fluorouracil?
There is a moderate interaction, so it may be acceptable with monitoring or timing changes — but check with your pharmacist first. Read the full details on this page and confirm with your pharmacist before combining them.
How serious is the Dimethylsulfoxide (dmso) and Fluorouracil interaction?
We rate it Moderate. This combination may require monitoring, a dose adjustment, or separating the times you take each one. Consult your pharmacist before using them together.

Written and reviewed by the HelloPharmacist editorial staff. Our editorial policy

Still Have a Question About Fluorouracil and Dimethylsulfoxide (dmso)?

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This information is for education only and is not a substitute for professional medical advice. Always check with your pharmacist or doctor before starting, stopping, or combining supplements and medications.