Drug & supplement interaction

Purple Loosestrife + Lapatinib

Lapatinib brand name: Tykerb.

No Known Interaction
Medically reviewed by · Updated June 2026 · Pair last verified Sep 20, 2026
The bottom line No known interaction

We found no known interaction between Purple Loosestrife and Lapatinib 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.

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Interaction report

Purple Loosestrife and Lapatinib

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 Lapatinib and Purple Loosestrife 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.

Worth understanding: our licensed dataset holds no drug-interaction record for Purple Loosestrife at all — not against Lapatinib, and not against any other medication we track. This verdict therefore rests on the absence of any recorded data, not on research that looked at this combination and found nothing. We cannot rule an interaction out.

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.

Purple Loosestrife safety at a glance

Purple Loosestrife overall Use caution Generally used in folk medicine, but human safety data are limited.
Pregnancy Avoid Not enough safety information, so it is best avoided.
Breastfeeding Avoid No reliable safety data, so avoid while breastfeeding.

Safety guidance is general; always confirm with your pharmacist or doctor for your situation.

Still wondering about combining Lapatinib and Purple Loosestrife? Ask Dr. Brian Staiger, PharmD, BCPS directly ›
What to actually watch for

What Lapatinib’s Own FDA Label Lists

This is not an interaction — none of it involves Purple Loosestrife. These are the most notable effects listed in the ADVERSE REACTIONS section of Lapatinib’s own FDA label, for the medication by itself. Knowing the drug’s own list makes it easier to work out the likely cause if something new turns up while you take both.

  • Diarrhea mentioned in 27.1% of FDA reports for Lapatinib
  • Acne
  • Mouth irritation or sores
  • Tiredness mentioned in 8.5% of FDA reports for Lapatinib
  • Vomiting mentioned in 7.8% of FDA reports for Lapatinib
  • A skin rash mentioned in 6.9% of FDA reports for Lapatinib
  • Nausea mentioned in 10.5% of FDA reports for Lapatinib

From the ADVERSE REACTIONS section of the FDA label for Lapatinib. Read the label on DailyMed › Where a percentage is shown, it is the share of 15,427 voluntary FDA FAERS reports for Lapatinib that mention that effect — a reporting proportion, not an incidence rate and not evidence the drug caused it. Purple Loosestrife’s licensed record lists no adverse effects our clinical vocabulary could match, so there is no Purple Loosestrife side to compare — that is a limit of the record, not a statement that Purple Loosestrife has no side effects.

Everything else you take

See Every Supplement That Interacts With Lapatinib

This page covers Purple Loosestrife only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Lapatinib page lists 143 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: Activated Charcoal (major), Grapefruit (major), St. John's Wort (major), Acacia Rigidula (moderate) and Adrafinil (moderate).

By severity: 3 major · 100 moderate · 40 minor.

From our pharmacist’s overview on the Lapatinib page

“Of the 143 supplements on file for lapatinib (Tykerb), nearly all press on the same point, the CYP3A4 enzyme that clears this HER2-targeted breast cancer drug. That deserves real caution, since lapatinib only works when its blood level stays in range.”

Reviewed by 2 · Jul 18, 2026

Open the Lapatinib interaction page

One more smart check

Taking Purple Loosestrife as Part of a Dietary Supplement Product? Check It for Interactions

We hold 26 real supplement products containing Purple Loosestrife, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Purple Loosestrife. Even though Purple Loosestrife itself has no known interaction with Lapatinib, 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 Purple Loosestrife and Lapatinib 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 Purple Loosestrife
Top half

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

29 days ago today
Medication Lapatinib
Steady interest

#2,362 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.
  • Freshness: we automatically re-check this combination every week — this pair was last verified September 20, 2026. The Purple Loosestrife and Lapatinib records this page draws on were last updated June 22, 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 Purple Loosestrife

What is Purple Loosestrife?

  • Diarrhea
  • Digestive upset
  • Minor wound care
  • Sore throat and mouth irritation
  • Menstrual-related complaints

Purple Loosestrife is a flowering wetland plant traditionally used for diarrhea and minor digestive or skin complaints, largely because of its astringent tannin content. Modern human studies are very limited, so its benefits are not well proven. If you are considering it, talk with your pharmacist or doctor first, and avoid it during pregnancy and breastfeeding.

Lythrum salicaria · Lythraceae · Aerial parts (flowering tops, leaves) · Tea, liquid extract, tincture, dried herb

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

Purple Loosestrife: dosing

There is no well-established standardized dose for Purple Loosestrife. Traditional use has involved teas and liquid extracts, but reliable dosing guidelines from clinical research are not available.If you choose to use a commercial product, follow the directions on the label and do not exceed them.

From our Purple Loosestrife monograph — the full record covers uses, side effects and every documented interaction.

Read the full Purple Loosestrife monograph & all interactions
Medication

About Lapatinib

What Is Lapatinib Used For?

Brand name: Tykerb

Lapatinib tablets — sold under the brand name Tykerb — are used to treat advanced or metastatic breast cancer in patients whose tumors overexpress the HER2 protein. They are always used in combination with another medicine, not alone.

Tykerb is approved in combination with capecitabine for HER2-positive advanced or metastatic breast cancer in patients who have already received prior treatment including an anthracycline, a taxane, and trastuzumab, and whose disease has progressed on trastuzumab. Tykerb is also approved in combination with letrozole for postmenopausal women with hormone receptor-positive, HER2-positive metastatic breast cancer when hormonal therapy is appropriate.

Most-Reported Side Effects for Lapatinib

From FAERS, the FDA’s public side-effect reporting system (15,427 reports, all brands). Reports are voluntary and are not proof the drug caused the effect.

Diarrhea 4,174 reports
Nausea 1,615 reports
Fatigue 1,305 reports
Vomiting 1,209 reports
Rash 1,061 reports
See full Lapatinib drug information
Keep checking

Other Drugs & Purple Loosestrife

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

0Major
0Moderate
0Minor
2,829No known interaction
2,829 No interaction
No interaction 2,829 drugs checked — show the list

We also checked Purple Loosestrife against these medications and found no known interaction in our sources. Open any page to confirm.

Showing the 60 most looked-up of 2,829 medications checked with no known interaction — see the full Purple Loosestrife list.

See the full Purple Loosestrife interactions page
See every supplement checked against Lapatinib, ranked by severity
Sources

Sources & How We Checked

We checked Purple Loosestrife against Lapatinib in the Natural Medicines interaction database and found no documented interaction on file. The medication overview comes from MedlinePlus, and supplement label details from the NIH Dietary Supplement Label Database.

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
Purple Loosestrife monograph › Uses, safety, and every drug interaction in one place Lapatinib supplement interactions › Every supplement checked against Lapatinib, ranked by severity Lapatinib 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 Purple Loosestrife and Lapatinib Together: Common Questions

Is it safe to take Purple Loosestrife with Lapatinib?
We do not list a known interaction between Purple Loosestrife and Lapatinib. 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.
Does Lapatinib interact with any supplements?
Yes. Lapatinib has documented interactions with 143 supplements in our database — Purple Loosestrife is not one of them. The Lapatinib interaction page linked on this page lists every one, ranked by severity.

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

Still Have a Question About Lapatinib and Purple Loosestrife?

Our pharmacists answer your medication & supplement questions — free.

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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.