Drug & supplement interaction

Vitamin C + Aspirin, Codeine Phosphate, Phenobarbital

Aspirin, Codeine Phosphate, Phenobarbital brand name: Phenaphen.

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

Vitamin C has a minor interaction with Aspirin, Codeine Phosphate, Phenobarbital. Acidification of the urine by vitamin C might increase aspirin levels.

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

Vitamin C and Aspirin, Codeine Phosphate, Phenobarbital

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

Minor

ASPIRIN

Acidification of the urine by vitamin C might increase aspirin levels.
It has been suggested that acidification of the urine by vitamin C could increase reabsorption of salicylates by the renal tubules, and increase plasma salicylate levels. However, short-term use of up to 6 grams daily of vitamin C does not seem to affect urinary pH or salicylate excretion, suggesting this interaction is not clinically significant.
Severity Minor 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 contains aspirin, and that's the piece vitamin C might touch. The thinking goes like this: vitamin C is acidic, and a more acidic urine could in theory let your kidneys hold onto more of the aspirin (salicylate) instead of flushing it out. If levels crept up, you might notice more typical aspirin effects like stomach upset, heartburn, or ringing in the ears.

Here's the reassuring part. When this was actually studied, even fairly high doses (up to 6 grams of vitamin C a day) didn't meaningfully change urine acidity or how much aspirin was cleared. So in real life this interaction looks unlikely to matter. Vitamin C shouldn't affect the codeine or phenobarbital parts. Still, check with your pharmacist before taking high-dose vitamin C regularly.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Hansten PD, Horn JR. Drug Interactions Analysis and Management. Vancouver, WA: Applied Therapeutics Inc., 1997 and updates.
  2. Mc Leod DC, Nahata MC. Inefficacy of ascorbic acid as a urinary acidifier (letter). N Engl J Med 1977;296:1413. DOI
  3. Hansten PD, Hayton WL. Effect of antacid and ascorbic acid on serum salicylate concentration. J Clin Pharmacol 1980;20:326-31. 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 Aspirin, Codeine Phosphate, Phenobarbital 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. Aspirin, Codeine Phosphate, Phenobarbital)
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 Aspirin, Codeine Phosphate, Phenobarbital

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 Aspirin, Codeine Phosphate, Phenobarbital, 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 Aspirin, Codeine Phosphate, Phenobarbital

This page covers Vitamin C only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Aspirin, Codeine Phosphate, Phenobarbital page lists 352 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), Asarabacca (major), Beer (major) and Danshen (major).

By severity: 12 major · 304 moderate · 36 minor.

From our pharmacist’s overview on the Aspirin, Codeine Phosphate, Phenobarbital page

“Alcohol is the entry I would flag first with Phenaphen (aspirin, codeine phosphate, phenobarbital): beer or wine layered onto codeine and phenobarbital can deepen sedation and, at worst, slow breathing. This medication deserves real caution with supplements.”

Reviewed by 2 · Jul 18, 2026

Open the Aspirin, Codeine Phosphate, Phenobarbital 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 Aspirin, Codeine Phosphate, Phenobarbital 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 Aspirin, Codeine Phosphate, Phenobarbital 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 Aspirin, Codeine Phosphate, Phenobarbital
Top 10%

#280 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 Aspirin, Codeine Phosphate, Phenobarbital, 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 Aspirin, Codeine Phosphate, Phenobarbital supplement interactions › Every supplement checked against Aspirin, Codeine Phosphate, Phenobarbital, 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 Aspirin, Codeine Phosphate, Phenobarbital Together: Common Questions

Can you take Vitamin C with Aspirin, Codeine Phosphate, Phenobarbital?
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 Aspirin, Codeine Phosphate, Phenobarbital 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 Aspirin, Codeine Phosphate, Phenobarbital and Vitamin C?

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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.