Drug & supplement interaction

Shepherd's Purse + Cetirizine

Cetirizine brand names: Cetirizine, Zyrtec, Quzyttir.

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

Shepherd's Purse has a moderate interaction with Cetirizine. Theoretically, concomitant use with drugs with sedative properties may cause additive effects and side effects.

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

Shepherd's Purse and Cetirizine

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

Moderate

CNS DEPRESSANTS

Why this applies to Cetirizine

Cetirizine falls under CNS DEPRESSANTS — the group Shepherd's Purse interacts with.

Theoretically, concomitant use with drugs with sedative properties may cause additive effects and side effects.
Severity Moderate Likelihood Possible Evidence D

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

Here's the thing to know about pairing shepherd's purse with cetirizine (Zyrtec). Cetirizine isn't a prodrug, so this isn't about how the herb changes its breakdown. Instead, the concern is simply additive drowsiness. Shepherd's purse has been reported to have mild sedative-type effects, and cetirizine, even though it's a newer antihistamine, can still make some people feel sleepy or foggy. Put the two together and you might feel a bit more tired than usual.

I'll be honest with you: this interaction is theoretical, based on how each is thought to work, not on strong human studies. So I wouldn't lose sleep over it. Just go easy on driving until you know how you feel, and check with your pharmacist or doctor if you take other calming products too.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Newall CA, Anderson LA, Philpson JD. Herbal Medicine: A Guide for Healthcare Professionals. London, UK: The Pharmaceutical Press, 1996.

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

Shepherd's Purse Also Interacts With Other Medications

Shepherd's Purse has 263 moderate known drug interactions in our database — the Cetirizine one above is one of them. If you take anything else, check it against the full list below.

Moderate 263 No known interaction 2,567 (incl. Cetirizine)
Taking anything else?

Check Another of Your Medications Against Shepherd's Purse

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

From our Q&A

Questions About Shepherd's Purse or Cetirizine

These are real questions from readers, answered by the pharmacists at HelloPharmacist — written by a person, not generated from a database. Each one covers Shepherd's Purse or Cetirizine, 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 Cetirizine

This page covers Shepherd's Purse only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Cetirizine page lists 100 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: 1,4-butanediol (major), Activated Charcoal (major), Beer (major), Gamma-hydroxybutyrate (ghb) (major) and Kava (major).

By severity: 7 major · 78 moderate · 15 minor.

From our pharmacist’s overview on the Cetirizine page

“Cetirizine (Zyrtec) treats allergies, but even this newer antihistamine can make some people drowsy, and that weak spot is where most of its 100 documented supplement interactions land. Seventy-eight of the ingredients on this page add their own sedative pull on top of the drug's, and 7 of the 100 rate major, so treat this list with re…”

Reviewed by 2 · Jul 18, 2026

Open the Cetirizine interaction page

One more smart check

Taking Shepherd's Purse as Part of a Dietary Supplement Product? Check It for Interactions

We hold 73 real supplement products containing Shepherd's Purse, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Shepherd's Purse. Your product may carry other ingredients that interact with Cetirizine too, on top of Shepherd's Purse — and those would not show on this page. Find your product and we’ll check every ingredient on its label:

How much people look this up

Where Shepherd's Purse and Cetirizine 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 Shepherd's Purse
Top half

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

29 days ago today
Medication Cetirizine
Top 25%

#409 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 Shepherd's Purse

What is Shepherd's Purse?

Shepherd's Purse
  • Heavy or prolonged menstrual bleeding
  • Minor bleeding (nosebleeds, wounds)
  • Mild diuretic
  • Digestive complaints
  • After-childbirth bleeding (traditional)

Shepherd's purse is a traditional herb most often used to help slow heavy menstrual bleeding and other minor bleeding, but solid human research is very limited. Because it may affect blood clotting, blood pressure, and the uterus, it should be avoided during pregnancy and used cautiously under professional guidance.

Read the full Shepherd's Purse monograph & all interactions
Medication

About Cetirizine Injection

What Is Cetirizine Injection Used For?

Brand names: Cetirizine, Zyrtec, Quzyttir

Quzyttir (cetirizine injection) is approved to treat acute urticaria — a sudden outbreak of hives — in adults and in children 6 months of age and older. It is given by intravenous (IV) injection in a medically supervised setting.

Quzyttir is not recommended for children under 6 years of age who have impaired kidney or liver function.

See full Cetirizine Injection drug information
Keep checking

Other Drugs & Shepherd's Purse

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

0Major
263Moderate
0Minor
2,566No known interaction
263 Moderate 2,566 No interaction
Moderate

263 interactions

Showing 60 of 263 moderate interactions — see all 263 on the Shepherd's Purse page.

No interaction 2,566 drugs checked — show the list

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

Showing the 60 most looked-up of 2,566 medications checked with no known interaction — see the full Shepherd's Purse list.

See the full Shepherd's Purse interactions page
See every supplement checked against Cetirizine, 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
Shepherd's Purse monograph › Uses, safety, and every drug interaction in one place Cetirizine supplement interactions › Every supplement checked against Cetirizine, ranked by severity Cetirizine 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 Shepherd's Purse and Cetirizine Together: Common Questions

Can you take Shepherd's Purse with Cetirizine?
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 Shepherd's Purse and Cetirizine 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 Cetirizine and Shepherd's Purse?

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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.