Drug & supplement interaction

Vitamin C + Indinavir

Indinavir brand name: Crixivan.

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

Vitamin C has a moderate interaction with Indinavir. Vitamin C can modestly reduce indinavir levels.

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

Vitamin C and Indinavir

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

Moderate

INDINAVIR (Crixivan)

Vitamin C can modestly reduce indinavir levels.
One pharmacokinetic study shows that taking vitamin C 1 gram orally once daily along with indinavir 800 mg orally three times daily reduces the area under the concentration-time curve of indinavir by 14%. The mechanism of this interaction is unknown, but it is unlikely to be clinically significant in most patients. The effect of higher doses of vitamin C on indinavir levels is unknown.
Severity Moderate 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: high-dose vitamin C can nudge your indinavir levels down a bit. In one study, folks taking 1 gram of vitamin C a day saw their indinavir exposure drop by about 14%. Indinavir works directly to keep HIV in check (it isn't a prodrug that needs activating), so lower levels mean a little less drug doing its job.

Honestly, a 14% dip is small and probably won't matter for most people. But because keeping HIV suppressed is so important, I'd still mention it. The real unknown is megadoses of vitamin C, since those weren't studied. The vitamin C you get from food or a daily multivitamin is unlikely to be a concern. Before starting any high-dose vitamin C, just run it by your pharmacist or doctor.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Slain D, Amsden JR, Khakoo RA, et al. Effect of high-dose vitamin C on the steady-state pharmacokinetics of the protease inhibitor indinavir in healthy volunteers. Pharmacotherapy 2005;25:165-70. PubMed
  2. Jalloh MA, Gregory PJ, Hein D, et al. Dietary supplement interactions with antiretrovirals: a systematic review. Int J STD AIDS. 2017 Jan;28(1):4-15. 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 100 moderate, 106 minor known drug interactions in our database — the Indinavir one above is one of them. If you take anything else, check it against the full list below.

Moderate 100 Minor 106 No known interaction 2,624 (incl. Indinavir)
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 Indinavir

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 Indinavir, 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 Indinavir

This page covers Vitamin C only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Indinavir page lists 150 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: Activated Charcoal (major), Grapefruit (major), St. John's Wort (major), Acacia Rigidula (moderate) and Adrafinil (moderate).

By severity: 3 major · 109 moderate · 38 minor.

From our pharmacist’s overview on the Indinavir page

“St. John's wort can drop indinavir (Crixivan) levels far enough to cause HIV treatment failure and viral resistance, which is why this list calls for real care before adding any supplement.”

Reviewed by 2 · Jul 18, 2026

Open the Indinavir 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 Indinavir 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 Indinavir 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 Indinavir
Top half

#1,110 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
Medication

About Indinavir

What Is Indinavir Used For?

Brand name: Crixivan

  • Indinavir is used along with other medications to treat human immunodeficiency virus (HIV) infection. Indinavir is in a class of medications called protease inhibitors. It works by decreasing the amount of HIV in the blood. Although indinavir does not cure HIV, it may decrease your chance of developing acquired immunodeficiency syndrome (AIDS) and HIV-related illnesses such as serious infections or cancer. Taking these medications along with practicing safer sex and making other lifestyle changes may decrease the risk of transmitting the HIV virus to other people.

See full Indinavir drug information
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
100Moderate
106Minor
2,623No known interaction
100 Moderate 106 Minor 2,623 No interaction
Moderate

100 interactions

Showing 60 of 100 moderate interactions — see all 100 on the Vitamin C page.

Minor

106 interactions

Showing 60 of 106 minor interactions — see all 106 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 Indinavir, 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 Indinavir supplement interactions › Every supplement checked against Indinavir, ranked by severity Indinavir drug information › The full plain-English guide to this medication 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 Indinavir Together: Common Questions

Can you take Vitamin C with Indinavir?
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 Vitamin C and Indinavir 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 Indinavir 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.