Drug & supplement interaction

St. John's Wort + Mechlorethamine Hydrochloride

Mechlorethamine Hydrochloride brand name: Valchlor.

No Known Interaction
Medically reviewed by · Updated July 2026 · Pair last verified Sep 13, 2026
The bottom line No known interaction

We found no known interaction between St. John's Wort and Mechlorethamine Hydrochloride in our sources. Absence of a documented interaction is not the same as proven safety, and does not guarantee one does not exist. Do not start, stop, or change a medication or supplement based on this page; confirm with your pharmacist or doctor first. Additionally, although there is no interaction, the two are separately associated with some of the same side effects, which would make a new symptom harder to attribute to one or the other.

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Interaction report

St. John's Wort and Mechlorethamine Hydrochloride

We checked these two against our interaction database. Here is what we found.

No Known Interaction Found

We did not find a documented interaction between Mechlorethamine Hydrochloride and St. John's Wort in our sources. This does not guarantee that the combination is completely free of risk — there is often limited research on supplements and herbal products, especially around drug interactions.

If you decide to take both, the practical routine is simple: add one new thing at a time and note the date you started it. If the combination is going to disagree with you, it usually shows in the first days to a couple of weeks — and a start date turns “I’ve been feeling off” into something a pharmacist can actually work with. Do not stop a prescribed medicine on your own.

Always talk with your pharmacist or doctor before making changes to your medications or supplements, particularly if you take several medications or have an ongoing health condition.

St. John's Wort safety at a glance

St. John's Wort overall Use caution Generally well tolerated short-term but has many serious drug interactions and can cause sun sensitivity.
Pregnancy Possibly Unsafe When used orally. Preliminary population research has found that taking St. John's wort while pregnant is associated with offspring that develop neural tube, ur... Read the full pregnancy detail
Breastfeeding Possibly Unsafe When used orally. Nursing infants of mothers who take St. John's wort have a greater chance of experiencing colic, drowsiness, and lethargy; avoid using. Read the full breastfeeding detail

Pregnancy & breastfeeding ratings are from Natural Medicines (Therapeutic Research Center) — the full detail is in the Special populations card below. Safety guidance is general; always confirm with your pharmacist or doctor for your situation.

Still wondering about combining Mechlorethamine Hydrochloride and St. John's Wort? Ask Dr. Brian Staiger, PharmD, BCPS directly ›
How we checked

Why No Interaction Is Listed for Mechlorethamine Hydrochloride

Interactions in our licensed database are recorded against drug classes, not just single drug names. Mechlorethamine Hydrochloride is filed under 2 classifications — alkylating agents, topical drugs. St. John's Wort has documented interactions with 47 drug classes — the most serious being alprazolam (xanax) (major), contraceptive drugs (major) and cyclosporine (neoral, sandimmune) (major) — and none of Mechlorethamine Hydrochloride’s classifications are among them.

Classification data comes from our licensed Natural Medicines dataset. A medication can belong to classes beyond those recorded there, so this describes how the check was run — it is not a safety guarantee.

Keep it in perspective

St. John's Wort Does Interact With Other Medications

St. John's Wort has 755 major, 388 moderate known drug interactions in our database — Mechlorethamine Hydrochloride isn’t one of them. If you take anything else, check it against the full list below.

Major 755 Moderate 388 No known interaction 1,687 (incl. Mechlorethamine Hydrochloride)
Taking anything else?

Check Another of Your Medications Against St. John's Wort

Covers the 2,830 medications we’ve checked against St. John's Wort. Pick one to open its full report.

What to actually watch for

No Interaction Found — But Data Suggests St. John's Wort and Mechlorethamine Hydrochloride May Share Several of the Same Side Effects

This is not an interaction. Neither one changes how your body handles the other, and nothing here says they react together. What our sources do show is that each has separately been linked to the effects below — so taking both can make those effects more likely to turn up, and harder to pin on one or the other if they do.

  • Itching reported in 24.3% of FDA reports for Mechlorethamine Hydrochloride Additional detail

    St. John's Wort

    “Both topical and chronic oral use of St. John's wort can cause photodermatitis. The average threshold dose range for an increased risk of photosensitivity appears to be 1.8-4 grams St. John's wort extract or 5-10 mg hypericin, daily. Lower doses might not cause this effect. For example, a single dose of St.”

    St. John's Wort · Natural Medicines adverse-effect record, reported in alopecia.

    6 sources cited
    1. 206. Gulick RM, McAuliffe V, Holden-Wiltse J, et al. Phase I studies of hypericin, the active compound in St. John's Wort, as an antiretroviral agent in HIV-infected adults. AIDS Clinical Trials Group Protocols 150 and 258. Ann Intern Med 1999;130:510-4. PubMed
    2. 620. Golsch S, Vocks E, Rakoski J, et al. [Reversible increase in photosensitivity to UV-B caused by St. John's wort extract]. Hautarzt 1997;48:249-52.
    3. 758. Upton R, ed. St. John's wort, Hypericum perforatum: Quality control, analytical and therapeutic monograph. Santa Cruz, CA: American Herbal Pharmacopoeia 1997;1-32.
    4. 4628. Schempp CM, Ludtke R, Winghofer B, Simon JC. Effect of topical application of hypericum perforatum extract on skin sensitivity to solar simulated radiation. Photodermatol Photoimmunol Photomed 2000;16:125-8.
    5. 4631. Jacobson JM, Feinman L, Liebes L, et al. Pharmacokinetics, safety, and antiviral effects of hypericin, a derivative of St. John's Wort plant, in patients with chronic hepatitis C virus infection. Antimicrob Agents Chemother 2001;45:517-24. PubMed
    6. 6477. Lane-Brown MM. Photosensitivity associated with herbal preparations of St. John's wort (Hypericum perforatum). Med J Aust 2000;172:302.

    Mechlorethamine Hydrochloride

    Listed in the ADVERSE REACTIONS section of the FDA label for Mechlorethamine Hydrochloride, and in voluntary FDA adverse-event reports. Read the label on DailyMed ›

  • A skin rash Additional detail

    St. John's Wort

    “Orally, St. John's wort is generally well tolerated.

    Most Common Adverse Effects:

    Orally: Diarrhea, dizziness, dry mouth, gastrointestinal discomfort (mild), fatigue, headache, insomnia, restlessness, and sedation.

    Topically: Skin rash and photodermatitis.

    Serious Adverse Effects (Rare):

    Orally: There have been rare case reports of suicidal ideation and psychosis after taking St. John's wort.”

    St. John's Wort · Natural Medicines adverse-effect record, reported in cluster headache.

    Mechlorethamine Hydrochloride

    Listed in the ADVERSE REACTIONS section of the FDA label for Mechlorethamine Hydrochloride. Read the label on DailyMed ›

Reported for St. John's Wort but not commonly for Mechlorethamine Hydrochloride: stomach upset, low blood pressure, erection problems and dependence or withdrawal symptoms.

Effects for Mechlorethamine Hydrochloride come from the ADVERSE REACTIONS section of its FDA label; effects for St. John's Wort come from the Natural Medicines adverse-effect record, quoted above. Where a percentage is shown, it is the share of 2,244 voluntary FDA FAERS reports for Mechlorethamine Hydrochloride that mention that effect — a reporting proportion, not an incidence rate and not evidence the drug caused it. Wording is matched across sources by our own clinical vocabulary, so treat this as a prompt to pay attention, not a diagnosis.

Special populations

St. John's Wort in Pregnancy & Breastfeeding

Pregnancy Possibly Unsafe

When used orally. Preliminary population research has found that taking St. John's wort while pregnant is associated with offspring that develop neural tube, urinary, and cardiovascular malformations. Subgroup analyses suggest that these risks may be higher when taking St. John's wort during the first trimester when compared with the second or third trimester. However, more research is needed to confirm these findings. Animal-model research also shows that constituents of St. John's wort might have teratogenic effects. Until more is known, St. John's wort should not be taken during pregnancy.

Lactation Possibly Unsafe

When used orally. Nursing infants of mothers who take St. John's wort have a greater chance of experiencing colic, drowsiness, and lethargy; avoid using.

DISCLAIMER: This tool is intended for informational purposes only, and should not be interpreted as specific medical advice. Patients should consult with a qualified healthcare provider before making decisions about therapies and/or health conditions.© 2026 Therapeutic Research Center

From our Q&A

Questions About St. John's Wort or Mechlorethamine Hydrochloride

These are real questions from readers, answered by the pharmacists at HelloPharmacist — written by a person, not generated from a database. Each one covers St. John's Wort or Mechlorethamine Hydrochloride, not necessarily both, but if one is close to what you were about to ask it will usually go further than a database entry can:

Not quite your question? Ask our pharmacists directly — it is free, there is no account required, and answers usually come back within 24 hours.

Everything else you take

See Every Supplement That Interacts With Mechlorethamine Hydrochloride

This page covers St. John's Wort only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Mechlorethamine Hydrochloride page lists 10 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: Acerola (moderate), Alpha-lipoic Acid (moderate), Coenzyme Q10 (moderate), Dimethylsulfoxide (dmso) (moderate) and Rose Hip (moderate).

By severity: 9 moderate · 1 minor.

From our pharmacist’s overview on the Mechlorethamine Hydrochloride page

“Mechlorethamine (Valchlor) is a chemotherapy gel applied to the skin for a form of lymphoma, and the 10 supplements on this page split into two groups. Seven are antioxidants, everyday products like vitamin C and turmeric, which in theory could blunt how well an alkylating chemotherapy drug works.”

Reviewed by 2 · Jul 18, 2026

Open the Mechlorethamine Hydrochloride interaction page

One more smart check

Taking St. John's Wort as Part of a Dietary Supplement Product? Check It for Interactions

We hold 1,159 real supplement products containing St. John's Wort, each one broken down to its full ingredient list — and combination products often carry several ingredients besides St. John's Wort. Even though St. John's Wort itself has no known interaction with Mechlorethamine Hydrochloride, another ingredient on your label might. Find your product and we’ll check every ingredient on its label:

How much people look this up

Where St. John's Wort and Mechlorethamine Hydrochloride 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 St. John's Wort
Top 25%

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

29 days ago today
Medication Mechlorethamine Hydrochloride
Steady interest

#1,502 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.

Where does our data come from?
  • Source: the Natural Medicines (TRC Healthcare) clinical database — the evidence-graded professional reference for herb & supplement interactions.
  • Citation library: 103,510 references behind our interaction content, 65,311 of them resolved to verified PubMed/DOI sources. See every St. John's Wort reference on this page ↓
  • Freshness: we automatically re-check this combination every week — this pair was last verified September 13, 2026. The St. John's Wort and Mechlorethamine Hydrochloride records this page draws on were last updated July 11, 2026.
  • What “no known interaction” means: no documented interaction in the sources above — not a guarantee of safety. Supplements are studied far less than prescription drugs, so we say exactly what the evidence supports, and nothing more.
Data structure & sourcing designed and verified by .
Supplement

About St. John's Wort

What is St. John's Wort?

St. John's Wort
  • Mild to moderate depression
  • Anxiety and stress
  • Sleep problems
  • Menopausal symptoms
  • Wound healing (topical)

St. John's wort is a well-studied herb most often used for mild to moderate depression, and some research suggests it may help with this. However, it has many serious interactions with prescription medicines and is not safe for everyone, so always talk to your pharmacist or doctor before taking it.

Hypericum perforatum · Hypericaceae · Flowering tops and aerial parts (leaves and flowers) · Capsules, tablets, standardized extracts, teas, tinctures, and topical oils

An interaction check asks whether these two react with each other — it does not ask whether St. John's Wort is a good idea for someone in your situation. Here is what our St. John's Wort record says about it on its own.

St. John's Wort: dosing

There is no single official dose for St. John's wort. Products vary widely in strength, and many studies use extracts standardized to a set amount of hypericin or hyperforin. Because of this, the right dose depends on the specific product.The safest approach is to follow the directions on the product label and to choose a standardized extract from a reputable brand. Effects on mood, if any, may take several weeks to appear.

From our St. John's Wort monograph — the full record covers uses, side effects and every documented interaction.

Read the full St. John's Wort monograph & all interactions
Medication

About Mechlorethamine Topical

What Is Mechlorethamine Topical Used For?

Brand name: Valchlor

Valchlor (mechlorethamine gel applied to the skin) is approved to treat Stage IA and IB mycosis fungoides-type cutaneous T-cell lymphoma — a slow-growing cancer that primarily affects the skin. It is used in patients who have already received at least one prior skin-directed treatment.

Most-Reported Side Effects for Mechlorethamine Hydrochloride

From FAERS, the FDA’s public side-effect reporting system (2,244 reports, all brands). Reports are voluntary and are not proof the drug caused the effect.

Pruritus 322 reports
Application site pruritus 224 reports
Application site erythema 220 reports
Application site pain 218 reports
Erythema 213 reports
See full Mechlorethamine Topical drug information
Keep checking

Other Drugs & St. John's Wort

Browse every other medication we’ve checked against St. John's Wort — both the ones with a known interaction and the ones without. Select any drug for the full detail.

755Major
388Moderate
0Minor
1,686No known interaction
755 Major 388 Moderate 1,686 No interaction
Major

755 interactions

Showing 60 of 755 major interactions — see all 755 on the St. John's Wort page.

Moderate

388 interactions

Showing 60 of 388 moderate interactions — see all 388 on the St. John's Wort page.

No interaction 1,686 drugs checked — show the list

We also checked St. John's Wort against these medications and found no known interaction in our sources. Open any page to confirm.

Showing the 60 most looked-up of 1,686 medications checked with no known interaction — see the full St. John's Wort list.

See the full St. John's Wort interactions page
See every supplement checked against Mechlorethamine Hydrochloride, ranked by severity
Evidence & sources

St. John's Wort References

The 152 references that drive our St. John's Wort monograph and interaction data, from the evidence-graded Natural Medicines (TRC Healthcare) database. Citations with a link open the study on PubMed or the publisher’s site.

  1. Miller LG. Herbal Medicinals: Selected clinical considerations focusing on known or potential drug-herb interactions. Arch Intern Med 1998;158:2200-11.
  2. Gulick RM, McAuliffe V, Holden-Wiltse J, et al. Phase I studies of hypericin, the active compound in St. John's Wort, as an antiretroviral agent in HIV-infected adults. AIDS Clinical Trials Group Protocols 150 and 258. Ann Intern Med 1999;130:510-4. PubMed
  3. O'Breasail AM, Argouarch S. Hypomania and St John's wort. Can J Psychiatry 1998;43:746-7.
  4. Johne A, Brockmoller J, Bauer S, et al. Pharmacokinetic interaction of digoxin with an herbal extract from St John's wort (Hypericum perforatum). Clin Pharmacol Ther 1999;66:338-45.
  5. Gordon JB. SSRIs and St. John's Wort: possible toxicity? Am Fam Physician 1998;57:950, 953.
  6. Golsch S, Vocks E, Rakoski J, et al. [Reversible increase in photosensitivity to UV-B caused by St. John's wort extract]. Hautarzt 1997;48:249-52.
  7. Bove GM. Acute neuropathy after exposure to sun in a patient treated with St. John's Wort. Lancet 1998;352:1121-2. PubMed
  8. Brockmoller J, Reum T, Bauer S, et al. Hypericin and pseudohypericin: pharmacokinetics and effects on photosensitivity in humans. Pharmacopsychiatry 1997;30:94-101. PubMed
  9. Upton R, ed. St. John's wort, Hypericum perforatum: Quality control, analytical and therapeutic monograph. Santa Cruz, CA: American Herbal Pharmacopoeia 1997;1-32.
  10. Muller WE, Singer A, Wonnemann M, et al. Hyperforin represents the neurotransmitter reuptake inhibiting constituent of hypericum extract. Pharmacopsychiatry 1998;31:16-21.
  11. Abul-Ezz SR, Barone GW, Gurley BJ, et al. Effect of herbal supplements on cyclosporine blood levels and associated acute rejection. Am Soc of Nephrol Ann Mtg, Toronto, CAN 2000;Oct. 11-16:abstract A3754.
  12. Piscitelli SC, Burstein AH, Chaitt D, et al. Indinavir concentrations and St John's wort. Lancet 2000;355:547-8. PubMed
  13. Yue QY, Bergquist C, Gerden B. Safety of St. John's wort (Hypericum perforatum). Lancet 2000;355:576-7. PubMed
  14. Ruschitzka F, Meier PJ, Turina M, et al. Acute heart transplant rejection due to Saint John's wort. Lancet 2000;355:548-9. PubMed
  15. Roberts JE, Wang RH, Tan IP, et al. Hypericin (active ingredient in St. John's wort) photo-oxidation of lens proteins. Photochem Photobiol 1999;69:42S.

Medication overviews come from MedlinePlus (NIH); supplement label data from the NIH Dietary Supplement Label Database. Content is written and reviewed by licensed HelloPharmacist pharmacists — see our data sources and editorial standards.

Pharmacist Counseling Corner

Taking St. John's Wort and Mechlorethamine Hydrochloride Together: Common Questions

Is it safe to take St. John's Wort with Mechlorethamine Hydrochloride?
We do not list a known interaction between St. John's Wort and Mechlorethamine Hydrochloride. That does not guarantee the combination is risk-free, so confirm with your pharmacist or doctor — especially if you take other medications or have a health condition.
Do St. John's Wort and Mechlorethamine Hydrochloride have any of the same side effects?
Yes — our sources link each of them separately to 2 of the same effects. That is not an interaction: neither changes how your body handles the other. It does mean that if one of those effects turns up, it can be harder to tell which one is behind it. They are listed on this page with the source behind each.
How was the St. John's Wort and Mechlorethamine Hydrochloride combination checked?
Interactions in our licensed database are recorded against drug classes. Mechlorethamine Hydrochloride is filed under 2 classifications, and St. John's Wort has documented interactions with 47 drug classes — none of Mechlorethamine Hydrochloride's classifications are among them. A medication can belong to classes beyond those recorded in our dataset, so this describes how the check was run rather than guaranteeing safety.
Does St. John's Wort interact with any other medications?
Yes. St. John's Wort has 1,143 documented drug interactions in our database — Mechlorethamine Hydrochloride is simply not one of them. If you take anything else, it is worth checking each one; they are all listed on this page.
Does Mechlorethamine Hydrochloride interact with any supplements?
Yes. Mechlorethamine Hydrochloride has documented interactions with 10 supplements in our database — St. John's Wort is not one of them. The Mechlorethamine Hydrochloride interaction page linked on this page lists every one, ranked by severity.

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

Where next

Keep Exploring

St. John's Wort monograph Uses, safety profile, and every drug interaction in one place Mechlorethamine Topical drug information The full plain-English guide to this medication Mechlorethamine Hydrochloride supplement interactions Every supplement checked against Mechlorethamine Hydrochloride, ranked by severity Supplement interaction checker Check any supplement or product against your medications Browse medications A–Z Every drug we’ve checked against herbs & supplements References The 152 citations behind this page Ask a pharmacist Free, personal answer from our licensed team

Still Have a Question About Mechlorethamine Hydrochloride and St. John's Wort?

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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.