Drug & supplement interaction

Holly + Hydroxyurea

Hydroxyurea brand names: Droxia, Hydrea, Siklos, Xromi.

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 Holly and Hydroxyurea 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

Holly and Hydroxyurea

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 Hydroxyurea and Holly 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 Holly at all — not against Hydroxyurea, 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.

Holly safety at a glance

Holly overall Use caution The berries are toxic if eaten, and there is little safety data on leaf preparations.
Pregnancy Unsafe When berries are ingested. There is insufficient reliable information available about the safety of holly leaves; avoid using. Read the full pregnancy detail
Breastfeeding Unsafe When berries are ingested. There is insufficient reliable information available about the safety of holly leaves; 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 Hydroxyurea and Holly? Ask Dr. Brian Staiger, PharmD, BCPS directly ›
What to actually watch for

No Interaction Found — But Data Suggests Holly and Hydroxyurea 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.

  • Diarrhea / Nausea / Vomiting reported in 6.7% of FDA reports for Hydroxyurea Additional detail

    Holly

    “Orally, ingestion of holly leaf can cause GI irritation, diarrhea, nausea, and vomiting (6,18). Holly leaf spines may tear or puncture skin or mucous membranes (6). Ingestion of as few as 2 holly berries can cause vomiting and diarrhea in small children (6). Ingestion of more than 5 holly berries can cause nausea, vomiting, and diarrhea (6,18). Ingestion of 20-30 holly berries can cause death (18).”

    Holly · Natural Medicines adverse-effect record, reported in diarrhea.

    2 sources cited
    1. 6. The Review of Natural Products by Facts and Comparisons. St. Louis, MO: Wolters Kluwer Co., 1999.
    2. 18. Gruenwald J, Brendler T, Jaenicke C. PDR for Herbal Medicines. 1st ed. Montvale, NJ: Medical Economics Company, Inc., 1998.

    “Orally, ingestion of holly leaf can cause GI irritation, diarrhea, nausea, and vomiting (6,18). Holly leaf spines may tear or puncture skin or mucous membranes (6). Ingestion of as few as 2 holly berries can cause vomiting and diarrhea in small children (6). Ingestion of more than 5 holly berries can cause nausea, vomiting, and diarrhea (6,18).”

    Holly · Natural Medicines adverse-effect record, reported in diarrhea.

    2 sources cited
    1. 6. The Review of Natural Products by Facts and Comparisons. St. Louis, MO: Wolters Kluwer Co., 1999.
    2. 18. Gruenwald J, Brendler T, Jaenicke C. PDR for Herbal Medicines. 1st ed. Montvale, NJ: Medical Economics Company, Inc., 1998.

    Hydroxyurea

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

Effects for Hydroxyurea come from the ADVERSE REACTIONS section of its FDA label; effects for Holly come from the Natural Medicines adverse-effect record, quoted above. Where a percentage is shown, it is the share of 21,027 voluntary FDA FAERS reports for Hydroxyurea 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

Holly in Pregnancy & Breastfeeding

Pregnancy And Lactation Unsafe

When berries are ingested. There is insufficient reliable information available about the safety of holly leaves; 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 Holly or Hydroxyurea

These are real questions from readers, answered by the pharmacists at HelloPharmacist — written by a person, not generated from a database. Each one covers Holly or Hydroxyurea, 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 Hydroxyurea

This page covers Holly only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Hydroxyurea page lists 18 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: Activated Charcoal (major), Coffee Charcoal (moderate), European Mandrake (moderate), Glucomannan (moderate) and Guar Gum (moderate).

By severity: 1 major · 7 moderate · 10 minor.

From our pharmacist’s overview on the Hydroxyurea page

“People take hydroxyurea (Droxia, Hydrea, Siklos, Xromi) for serious reasons, most often sickle cell disease or certain blood cancers, and it only works if a steady dose reaches the bloodstream. That is exactly what nearly all 18 supplements listed here can undermine, so this page earns real vigilance rather than a skim.”

Reviewed by 2 · Jul 18, 2026

Open the Hydroxyurea interaction page

One more smart check

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

We hold 11 real supplement products containing Holly, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Holly. Even though Holly itself has no known interaction with Hydroxyurea, 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 Holly and Hydroxyurea 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 Holly
Steady interest

#1,324 of 1,452 supplements looked up here in the last 7 days

29 days ago today
Medication Hydroxyurea
Top 5%

#40 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 Holly reference on this page ↓
  • Freshness: we automatically re-check this combination every week — this pair was last verified September 13, 2026. The Holly and Hydroxyurea records this page draws on were last updated July 10, 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 Holly

What is Holly?

  • Fever
  • Cough and chest congestion
  • Joint pain (traditional use)
  • Digestive complaints
  • Mild diuretic

Holly (Ilex aquifolium) is a common ornamental shrub whose bright red berries are poisonous and should never be eaten. There is very little reliable human evidence supporting any health benefit of holly leaves, and because of safety concerns it is generally best avoided as a supplement unless guided by a knowledgeable healthcare professional.

Ilex aquifolium · Aquifoliaceae · Leaves and berries (and bark in some traditions) · Dried leaf tea, tinctures, and homeopathic preparations; berries are not used as a supplement

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

Holly: dosing

There is no established or standardized dose for holly, because it has not been properly studied as a medicine. We cannot provide a safe recommended amount.If you choose to use a commercial holly product despite the limited evidence, follow the directions on the label exactly and never exceed them.

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

Read the full Holly monograph & all interactions
Medication

About Hydroxyurea

What Is Hydroxyurea Used For?

Brand names: Droxia, Hydrea, Siklos, Xromi

Hydroxyurea is used for several serious conditions. Droxia, Siklos, and Xromi are each indicated to reduce the frequency of painful crises and reduce the need for blood transfusions in patients with sickle cell anemia who have recurrent moderate to severe painful crises. Siklos is approved for adults and children 2 years and older; Xromi is approved for children 6 months and older; Droxia is approved for adults.

Hydrea capsules and Hydroxyurea capsules are indicated for resistant chronic myeloid leukemia and for locally advanced squamous cell carcinomas of the head and neck (excluding the lip) when used together with chemoradiation.

Most-Reported Side Effects for Hydroxyurea

From FAERS, the FDA’s public side-effect reporting system (21,027 reports, all brands). Reports are voluntary and are not proof the drug caused the effect.

Fatigue 1,548 reports
Sickle cell anaemia with crisis 1,486 reports
Diarrhea 1,408 reports
Nausea 1,306 reports
Headache 1,068 reports
See full Hydroxyurea drug information
Keep checking

Other Drugs & Holly

Browse every other medication we’ve checked against Holly — 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 Holly 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 Holly list.

See the full Holly interactions page
See every supplement checked against Hydroxyurea, ranked by severity
Evidence & sources

Holly References

The 2 references that drive our Holly 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. The Review of Natural Products by Facts and Comparisons. St. Louis, MO: Wolters Kluwer Co., 1999.
  2. Gruenwald J, Brendler T, Jaenicke C. PDR for Herbal Medicines. 1st ed. Montvale, NJ: Medical Economics Company, Inc., 1998.

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 Holly and Hydroxyurea Together: Common Questions

Is it safe to take Holly with Hydroxyurea?
We do not list a known interaction between Holly and Hydroxyurea. 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 Holly and Hydroxyurea have any of the same side effects?
Yes — our sources link each of them separately to 3 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.
Does Hydroxyurea interact with any supplements?
Yes. Hydroxyurea has documented interactions with 18 supplements in our database — Holly is not one of them. The Hydroxyurea 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

Holly monograph Uses, safety profile, and every drug interaction in one place Hydroxyurea drug information The full plain-English guide to this medication Hydroxyurea supplement interactions Every supplement checked against Hydroxyurea, 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 2 citations behind this page Ask a pharmacist Free, personal answer from our licensed team

Still Have a Question About Hydroxyurea and Holly?

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.