Drug & supplement interaction

Gardenia + Phenolphthalein

Phenolphthalein brand names: Modane, Evac-Q-Tab, Modane Mild.

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

Gardenia has a moderate interaction with Phenolphthalein. Theoretically, gardenia might increase the effects and adverse effects of stimulant laxatives.

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

Gardenia and Phenolphthalein

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

Moderate

STIMULANT LAXATIVES

Why this applies to Phenolphthalein

Phenolphthalein falls under STIMULANT LAXATIVES — the group Gardenia interacts with.

Theoretically, gardenia might increase the effects and adverse effects of stimulant laxatives.
Animal research shows that geniposide, a glucoside found in gardenia fruit, may function as a laxative and cause diarrhea when taken orally.
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 simple version: phenolphthalein is a stimulant laxative, meaning it gets your bowels moving by irritating the intestinal lining. Gardenia fruit contains a compound called geniposide that, at least in animal studies, seems to act as a laxative too. So the worry is that taking both together could stack their effects and push things too far in the same direction.

In real life that might mean more cramping, watery diarrhea, urgency, and over time a risk of dehydration or losing important electrolytes like potassium. I want to be honest though, this concern comes only from lab and animal research, not human studies, so it's more of a theoretical caution than a proven problem. Still, it's worth running past your pharmacist or doctor before pairing them.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Yamauchi, K., Fujimoto, N., Kuwano, S., Inouye, H., and Inoue, K. The mechanism of purgative action of geniposide, an iridoid glucoside of the fruit of Gardenia, in mice. Planta Med 1976;30(1):39-47.

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

Gardenia Also Interacts With Other Medications

Gardenia has 20 moderate known drug interactions in our database — the Phenolphthalein one above is one of them. If you take anything else, check it against the full list below.

Moderate 20 No known interaction 2,810 (incl. Phenolphthalein)
Taking anything else?

Check Another of Your Medications Against Gardenia

Covers the 2,830 medications we’ve checked against Gardenia. Pick one to open its full report.

Everything else you take

See Every Supplement That Interacts With Phenolphthalein

This page covers Gardenia only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Phenolphthalein page lists 46 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: Activated Charcoal (major), Jalap (major), Oleander (major), Alder Buckthorn (moderate) and Aloe (moderate).

By severity: 3 major · 34 moderate · 9 minor.

From our pharmacist’s overview on the Phenolphthalein page

“Phenolphthalein is a stimulant laxative itself, and that is the heart of the problem with these combinations. Most of the herbs on file, jalap being one, act the same way, so pairing them can drain fluid and potassium quickly.”

Reviewed by 2 · Jul 18, 2026

Open the Phenolphthalein interaction page

One more smart check

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

We hold 240 real supplement products containing Gardenia, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Gardenia. Your product may carry other ingredients that interact with Phenolphthalein too, on top of Gardenia — 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 Gardenia and Phenolphthalein 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 Gardenia
Steady interest

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

29 days ago today
Medication Phenolphthalein
Top half

#1,101 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 Gardenia

What is Gardenia?

Gardenia
  • Liver and digestive complaints
  • Fever and inflammation
  • Anxiety, restlessness, and trouble sleeping
  • Blood pressure and blood sugar support (traditional)
  • Natural food and fabric coloring

Gardenia fruit has a long history in traditional Chinese medicine and is also used as a natural food coloring. While early lab and animal studies are interesting, strong human evidence for its health benefits is lacking, so talk with your pharmacist or doctor before using it as a supplement.

Read the full Gardenia monograph & all interactions
Keep checking

Other Drugs & Gardenia

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

0Major
20Moderate
0Minor
2,809No known interaction
20 Moderate 2,809 No interaction
Moderate

20 interactions

No interaction 2,809 drugs checked — show the list

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

Showing the 60 most looked-up of 2,809 medications checked with no known interaction — see the full Gardenia list.

See the full Gardenia interactions page
See every supplement checked against Phenolphthalein, 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
Gardenia monograph › Uses, safety, and every drug interaction in one place Phenolphthalein supplement interactions › Every supplement checked against Phenolphthalein, 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 Ask a pharmacist › Free, personal answer from our licensed team
Pharmacist Counseling Corner

Taking Gardenia and Phenolphthalein Together: Common Questions

Can you take Gardenia with Phenolphthalein?
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 Gardenia and Phenolphthalein 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 Phenolphthalein and Gardenia?

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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.