Drug & supplement interaction

Vitamin C + Acetaminophen, Dextromethorphan, Guaifenesin, Phenylephrine

Acetaminophen, Dextromethorphan, Guaifenesin, Phenylephrine brand name: Conar-A.

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

Vitamin C has a minor interaction with Acetaminophen, Dextromethorphan, Guaifenesin, Phenylephrine. High-dose vitamin C might slightly prolong the clearance of acetaminophen.

Read the full interaction report
SeverityMinor
LikelihoodProbable
EvidenceB
What do Severity, Likelihood & Evidence mean?
Know someone taking this? Share
Facebook Post Reddit Email
On this page
Interaction report

Vitamin C and Acetaminophen, Dextromethorphan, Guaifenesin, Phenylephrine

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

Minor

ACETAMINOPHEN (Tylenol, others)

High-dose vitamin C might slightly prolong the clearance of acetaminophen.
A small pharmacokinetic study in healthy volunteers shows that taking high-dose vitamin C (3 grams) 1.5 hours after taking acetaminophen 1 gram slightly increases the apparent half-life of acetaminophen from around 2.3 hours to 3.1 hours. Ascorbic acid competitively inhibits sulfate conjugation of acetaminophen. However, to compensate, elimination of acetaminophen glucuronide and unconjugated acetaminophen increases. This effect is not likely to be clinically significant.
Severity Minor Likelihood Probable Evidence B

Interaction 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..

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

Here's the gist for your Conar-A, which contains acetaminophen (the same active ingredient as Tylenol) along with a cough suppressant, an expectorant, and a decongestant. A small study found that a big dose of vitamin C (around 3 grams) can slow how fast your body clears acetaminophen just a little, nudging its half-life from about 2.3 hours up to 3.1 hours. Vitamin C gently competes with one of the pathways the liver uses to process acetaminophen.

The good news is that researchers found this effect tiny and not clinically meaningful. At normal doses you shouldn't notice anything. The bigger thing with any acetaminophen product is simply not exceeding the daily limit. If you take high-dose vitamin C regularly, mention it to your pharmacist.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Houston JB, Levy G. Drug biotransformation interactions in man VI: Acetaminophen and ascorbic acid. J Pharm Sci 1976;65:1218-21. 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

Vitamin C Also Interacts With Other Medications

Vitamin C has 101 moderate, 105 minor known drug interactions in our database — the Acetaminophen, Dextromethorphan, Guaifenesin, Phenylephrine one above is one of them. If you take anything else, check it against the full list below.

Moderate 101 Minor 105 No known interaction 2,624 (incl. Acetaminophen, Dextromethorphan, Guaifenesin, Phenylephrine)
Taking anything else?

Check Another of Your Medications Against Vitamin C

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

From our Q&A

Questions About Vitamin C or Acetaminophen, Dextromethorphan, Guaifenesin, Phenylephrine

These are real questions from readers, answered by the pharmacists at HelloPharmacist — written by a person, not generated from a database. Each one covers Vitamin C or Acetaminophen, Dextromethorphan, Guaifenesin, Phenylephrine, 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 Acetaminophen, Dextromethorphan, Guaifenesin, Phenylephrine

This page covers Vitamin C only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Acetaminophen, Dextromethorphan, Guaifenesin, Phenylephrine page lists 261 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: Activated Charcoal (major), Asarabacca (major), Beer (major), Ephedra (major) and Grapefruit (major).

By severity: 12 major · 206 moderate · 43 minor.

From our pharmacist’s overview on the Acetaminophen, Dextromethorphan, Guaifenesin, Phenylephrine page

“Picture the week someone takes Conar-A (acetaminophen, dextromethorphan, guaifenesin, phenylephrine): a miserable cold, coffee to push through, maybe wine at night or an herbal remedy on top. Those habits are exactly where this list turns serious.”

Reviewed by 2 · Jul 18, 2026

Open the Acetaminophen, Dextromethorphan, Guaifenesin, Phenylephrine interaction page

One more smart check

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

We hold 36,382 real supplement products containing Vitamin C, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Vitamin C. Your product may carry other ingredients that interact with Acetaminophen, Dextromethorphan, Guaifenesin, Phenylephrine too, on top of Vitamin C — 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 Vitamin C and Acetaminophen, Dextromethorphan, Guaifenesin, Phenylephrine 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 Vitamin C
Most looked up

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

29 days ago today
Medication Acetaminophen, Dextromethorphan, Guaifenesin, Phenylephrine
Top 10%

#190 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 Vitamin C

What is Vitamin C?

  • Common cold and immune support
  • Antioxidant support
  • Skin health and collagen formation
  • Wound healing
  • Preventing or treating scurvy
  • Improving iron absorption

Vitamin C (ascorbic acid) is an essential nutrient your body needs but cannot make, so you must get it from food or supplements. It's important for immune function, collagen, and acts as an antioxidant, but taking large doses doesn't prevent colds for most people and may cause stomach upset. Most people get enough from a balanced diet, so check with your pharmacist or doctor before taking high-dose supplements.

Read the full Vitamin C monograph & all interactions
Keep checking

Other Drugs & Vitamin C

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

0Major
101Moderate
105Minor
2,623No known interaction
101 Moderate 105 Minor 2,623 No interaction
Moderate

101 interactions

Showing 60 of 101 moderate interactions — see all 101 on the Vitamin C page.

Minor

105 interactions

Showing 60 of 105 minor interactions — see all 105 on the Vitamin C page.

No interaction 2,623 drugs checked — show the list

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

Showing the 60 most looked-up of 2,623 medications checked with no known interaction — see the full Vitamin C list.

See the full Vitamin C interactions page
See every supplement checked against Acetaminophen, Dextromethorphan, Guaifenesin, Phenylephrine, 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
Vitamin C monograph › Uses, safety, and every drug interaction in one place Acetaminophen, Dextromethorphan, Guaifenesin, Phenylephrine supplement interactions › Every supplement checked against Acetaminophen, Dextromethorphan, Guaifenesin, Phenylephrine, 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 Vitamin C and Acetaminophen, Dextromethorphan, Guaifenesin, Phenylephrine Together: Common Questions

Can you take Vitamin C with Acetaminophen, Dextromethorphan, Guaifenesin, Phenylephrine?
There is only a minor interaction, which is usually not serious. Read the full details on this page and confirm with your pharmacist before combining them.
How serious is the Vitamin C and Acetaminophen, Dextromethorphan, Guaifenesin, Phenylephrine interaction?
We rate it Minor. This interaction is generally not clinically significant, but it remains worth noting and discussing with your pharmacist.

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

Still Have a Question About Acetaminophen, Dextromethorphan, Guaifenesin, Phenylephrine and Vitamin C?

Our pharmacists answer your medication & supplement questions — free.

Ask a pharmacist

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.