Drug & supplement interaction

St. John's Wort + Guaifenesin, Theophylline

Guaifenesin, Theophylline brand names: Mudrane GG-2, Bronchial, Theolair-Plus, Quibron, Quibron-300.

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

Guaifenesin, Theophylline falls into 2 drug categories that St. John's Wort can interact with; the most serious is rated moderate. St. John's wort may increase the metabolism and reduce the levels of CYP1A2 substrates.

Read the full interaction report
SeverityModerate
LikelihoodPossible
Interactions2
EvidenceB
What do Severity, Likelihood & Evidence mean?
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Interaction report

St. John's Wort and Guaifenesin, Theophylline

These two interact in 2 distinct ways. Each one is explained separately below.

Why Are There 2 Interactions?

St. John's Wort interacts with whole categories of medication. Guaifenesin, Theophylline falls into 2 of those categories, so it can interact with St. John's Wort in 2 different ways. We’ve listed each one below — your overall risk is driven by the most serious of them (Moderate).

Moderate

CYTOCHROME P450 1A2 (CYP1A2) SUBSTRATES

1 of 2

Why this applies to Guaifenesin, Theophylline

Guaifenesin, Theophylline falls under CYTOCHROME P450 1A2 (CYP1A2) SUBSTRATES — the group St. John's Wort interacts with.

St. John's wort may increase the metabolism and reduce the levels of CYP1A2 substrates.
Clinical and in vitro research shows that St. John's wort induces CYP1A2, but to a lesser extent than CYP3A4.
Severity Moderate Likelihood Possible Evidence B

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

This combo product pairs guaifenesin (a simple mucus thinner) with theophylline, the part that matters here. Theophylline relaxes your airways to help you breathe, but it's a tricky drug with a narrow safe range. Your liver clears it using an enzyme called CYP1A2. St. John's wort can speed up that enzyme, which tends to flush theophylline out of your body faster and lower its levels.

In plain terms, your theophylline may not work as well, so you could notice more wheezing, coughing, or shortness of breath. Because even small swings in theophylline matter, please don't add or stop St. John's wort on your own. Talk with your pharmacist or doctor first, since your dose or blood levels may need checking.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Henderson L, Yue QY, Bergquist C, et al. St John's wort (Hypericum perforatum): drug interactions and clinical outcomes. Br J Clin Pharmacol 2002;54:349-56..
  2. Foster BC, Vandenhoek S, Hana J, et al. In vitro inhibition of human cytochrome P450-mediated metabolism of marker substrates by natural products. Phytomedicine 2003;10:334-42.. PubMed
  3. Van Strater, A. C. and Bogers, J. P. Interaction of St John's wort (Hypericum perforatum) with clozapine. Int.Clin.Psychopharmacol. 2012;27(2):121-124. PubMed
  4. Haron MH, Dale O, Martin K, et al. Evaluation of the Herb-Drug Interaction Potential of Commonly Used Botanicals on the US Market with Regard to PXR- and AhR-Mediated Influences on CYP3A4 and CYP1A2. J Diet Suppl 2022. PubMed
Minor

THEOPHYLLINE

2 of 2

Guaifenesin, Theophylline also falls under THEOPHYLLINE.

St. John's wort might decrease the levels of theophylline, although this effect might not be clinically relevant.
St. John's wort does not seem to significantly affect theophylline pharmacokinetics. There is a single case report of a possible interaction with theophylline. A patient who smoked and was taking 11 other drugs experienced an increase in theophylline levels after discontinuation of St. John's wort. This increase has been attributed to a rebounding of theophylline serum levels after St. John's wort was no longer present to induce metabolism via cytochrome P450 1A2 (CYP1A2). However, studies in healthy volunteers show that St. John's wort is unlikely to affect theophylline to any clinically significant degree.
Severity Minor Likelihood Unlikely Evidence D

Interaction has been demonstrated in animal or in lab research but has been shown not to occur in humans..

Dr. Brian Staiger, PharmD, BCPS
Dr. Brian Staiger explains PharmD, Clinical Pharmacist

Here's the gist for this combo product. The guaifenesin part just loosens mucus and isn't really involved here. The piece to watch is theophylline, which opens up your airways but has a fairly narrow safe range. In theory, St. John's wort can speed up a liver enzyme (CYP1A2) that clears theophylline, which could nudge your levels down and make the medicine work a little less well over time.

The good news is that the evidence here is weak. Studies in healthy people show little real effect, and the one report of a problem involved a smoker taking many other drugs. So for most people this is unlikely to matter much. Still, because theophylline is finicky, please check with your pharmacist or doctor before starting or stopping St. John's wort.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Nebel A, Schneider BJ, Baker RA, et al. Potential metabolic interaction between St. John's wort and theophylline. Ann Pharmacother 1999;33:502. PubMed
  2. Schulz V. Incidence and clinical relevance of the interactions and side effects of Hypericum preparations. Phytomedicine 2001;8:152-60.
  3. Henderson L, Yue QY, Bergquist C, et al. St John's wort (Hypericum perforatum): drug interactions and clinical outcomes. Br J Clin Pharmacol 2002;54:349-56..
  4. Morimoto T, Kotegawa T, Tsutsumi K, et al. Effect of St. John's wort on the pharmacokinetics of theophylline in healthy volunteers. J Clin Pharmacol 2004;44:95-101. PubMed

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

St. John's Wort Also Interacts With Other Medications

St. John's Wort has 756 major, 386 moderate known drug interactions in our database — the Guaifenesin, Theophylline one above is among them. If you take anything else, check it against the full list below.

Major 756 Moderate 386 No known interaction 1,688 (incl. Guaifenesin, Theophylline)
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.

From our Q&A

Questions About St. John's Wort or Guaifenesin, Theophylline

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 Guaifenesin, Theophylline, 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 Guaifenesin, Theophylline

This page covers St. John's Wort only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Guaifenesin, Theophylline page lists 126 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: Activated Charcoal (major), Ephedra (major), Sida Cordifolia (major), Adrafinil (moderate) and African Wild Potato (moderate).

By severity: 3 major · 89 moderate · 34 minor.

Open the Guaifenesin, Theophylline 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. Your product may carry other ingredients that interact with Guaifenesin, Theophylline too, on top of St. John's Wort — 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 St. John's Wort and Guaifenesin, Theophylline 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%

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

29 days ago today
Medication Guaifenesin, Theophylline
Top 10%

#215 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 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.

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

756Major
386Moderate
0Minor
1,687No known interaction
756 Major 386 Moderate 1,687 No interaction
Major

756 interactions

Showing 60 of 756 major interactions — see all 756 on the St. John's Wort page.

Moderate

386 interactions

Showing 60 of 386 moderate interactions — see all 386 on the St. John's Wort page.

No interaction 1,687 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 1,687 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 Guaifenesin, Theophylline, 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
St. John's Wort monograph › Uses, safety, and every drug interaction in one place Guaifenesin, Theophylline supplement interactions › Every supplement checked against Guaifenesin, Theophylline, 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 St. John's Wort and Guaifenesin, Theophylline Together: Common Questions

Can you take St. John's Wort with Guaifenesin, Theophylline?
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.
Why are there 2 interactions listed for St. John's Wort and Guaifenesin, Theophylline?
Guaifenesin, Theophylline belongs to more than one drug category, and St. John's Wort interacts with each of those categories a little differently. We list every one so nothing is missed — your overall risk is driven by the most serious of them.
How serious is the St. John's Wort and Guaifenesin, Theophylline 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 Guaifenesin, Theophylline 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.