Written by Jill Barat, PharmD | Reviewed by Rachel Feaster, PharmD, BCOP, BCPS

Published on November 19, 2024print_outlinedemail_outlined

Key takeaways:

• Even though vitamin C supplements are sold over the counter, they still have drug interactions to be aware of. It’s best to check with your healthcare team before starting a vitamin C supplement to make sure it’s a safe option for you.
• Vitamin C supplements can also lead to high aluminum levels if you take them with antacids that contain aluminum. They may also interact with nonsteroidal anti-inflammatory drugs (NSAIDs) and medications that contain estrogen.
• Other medications may not work as well if you take them along with vitamin C supplements. This includes statins, niacin, and warfarin. Vitamin C supplements may also interfere with the HIV medication indinavir (Crixivan) and certain chemotherapy treatments. 

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Vitamin C

Table of contents

Aluminum-containing antacids

Chemotherapy

Estrogen

Indinavir

Cholesterol meds

Warfarin

NSAIDs

Bottom line

References

GoodRx Health

Vitamin C (ascorbic acid) helps build collagen, improves iron absorption, and is a strong antioxidant. Your body can’t make vitamin C, so you absorb it from the food and drinks you consume. Most people get enough vitamin C from their regular diet. But if your vitamin C levels are low, your healthcare team may suggest a vitamin C supplement. Vitamin C supplements are also popular during cold and flu season (despite the fact that there’s not much evidence they do much to keep you healthy).

If you’re taking vitamin C, you should be aware that it has drug interactions, just like other medications and supplements. Here, we’ll look at seven vitamin C interactions you should know about.

Good to know: The interactions described below are related to vitamin C supplements. The vitamin C in your diet doesn’t have the same effects in most cases. So you don’t need to change what you’re eating unless your healthcare team recommends it.

1. Antacids that contain aluminum

Vitamin C supplements can interact with antacids that contain aluminum. This is because vitamin C can increase how much aluminum your body absorbs from these medications. High aluminum levels can cause weakness, confusion, and even seizures in severe cases. Kidney problems can raise the risk of this reaction. 

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Examples of antacids that contain aluminum include:

• Mylanta
• Gaviscon
• Antacid M

To avoid this interaction, it’s best to take a vitamin C supplement at least 2 hours before or at least 4 hours after any of these antacids. You could also try a different antacid that doesn’t contain aluminum, such as Tums or Rolaids. They contain calcium carbonate instead.

2. Chemotherapy

There’s some concern that vitamin C supplements may interact with certain chemotherapy medications. Vitamin C may help protect cancer cells and make certain chemotherapy treatments less effective. Combining high doses of vitamin C with some types of chemotherapy may also raise the risk of side effects, disrupt treatment, and allow cancer to worsen. We don’t know for sure how risky this interaction is. But it’s still a good idea to speak with your cancer care team before taking vitamin C or any other supplements during your cancer treatment.

3. Estrogen

It’s possible that vitamin C may increase estrogen levels if you take it with a medication that contains estrogen. It’s not clear why this happens, but vitamin C may interfere with how estrogen is broken down and cleared from the body. If your estrogen level goes too high, it can lead to side effects, such as mood swings and sleep issues. It can also raise the risk of thyroid problems, blood clots, and hormone-sensitive cancers such as breast cancer.

Common medications that contain estrogen include:

• Hormonal birth control
• Menopause hormonal therapy
• Medications used to help improve fertility
• Medications used as part of gender-affirming hormone therapy

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Studies show mixed results when it comes to an interaction between birth control pills and vitamin C. But it’s still best to talk to your healthcare team if you’re taking a medication that contains estrogen before taking a vitamin C supplement.

4. Indinavir

Indinavir (Crixivan) is a protease inhibitor that treats HIV. Vitamin C can make indinvair less effective, which raises the risk of your HIV infection being undertreated or developing resistance to treatment. If HIV isn’t treated properly, the risk of the infection spreading or worsening becomes much greater. So it’s best to avoid taking vitamin C supplements if indinavir is part of your treatment plan.

5. Statins and niacin

Statins and niacin are medications that treat high cholesterol levels. One study showed that vitamin C supplements may reduce how well a medication containing a combination of simvastatin and niacin works. Specifically, it prevented an increase in HDL (“good”) cholesterol levels.

It’s not clear whether the same interaction can happen if you take vitamin C with either of these medications separately. But it’s a good idea to let your prescriber know if you’re taking vitamin C if you’re also taking niacin or a statin. They can keep an eye on your cholesterol levels and let you know if vitamin C is interfering with your medication.

6. Warfarin

Warfarin (Coumadin, Jantoven) is an anticoagulant (blood thinner) that interacts with many medications, including vitamin C. High-dose vitamin C supplements (1 gram or more) may make warfarin less effective. This can increase your risk of developing a blood clot.

In most cases, your prescriber will adjust your warfarin dosage based on your regular routine. This includes the food you eat and your daily medications and supplements. You shouldn’t make any changes — including stopping or starting a vitamin C supplement — without talking to your healthcare team first. They can form a plan to monitor and adjust your warfarin dosage if needed while you make any necessary changes. This helps reduce the risk of blood clots or bleeding events that could be caused by the change you’re making.

7. NSAIDs

Nonsteroidal anti-inflammatory drugs (NSAIDs) include common pain and fever medications such as ibuprofen (Advil, Motrin) and naproxen (Aleve). Some NSAIDs are also available by prescription. Combining large doses of vitamin C and an NSAID may raise the risk of certain kidney problems.

It’s not clear how risky this interaction is. If you’re taking vitamin C and need to take one of these pain medications now and then, it isn’t likely to cause a problem. But if you need to take a NSAID long term, let your prescriber know you’re taking vitamin C. They may want you to stop taking it or reduce your dosage.

Long-term use of NSAIDs might also increase how much vitamin C your body gets rid of. This could make it harder for you to keep your vitamin C levels up, even if you’re taking a vitamin C supplement.

The bottom line

Vitamin C is a common over-the-counter (OTC) supplement. Even though it’s a natural vitamin found in your diet, vitamin C supplements can interact with the medications you’re taking. It’s best to check with your healthcare team before taking a vitamin C supplement to make sure it’s a safe option for you.

Vitamin C supplements may interact with medications that contain estrogen and antacids that contain aluminum. They may also raise the risk of kidney problems if taken with nonsteroidal anti-inflammatory drugs (NSAIDs).

Other medications may become less effective if you take them with a vitamin C supplement. These include warfarin, statins, and niacin. Vitamin C can also interfere with indinavir (Crixivan), an antiviral that treats HIV, and certain chemotherapy treatments.

Why trust our experts?

Written by:

Jill Barat, PharmD

Jill Barat, PharmD has nearly 10 years of experience as a pharmacist, including serving as the pharmacist in charge at an independent sterile and non-sterile compounding pharmacy. She also worked as the head of medical content for a telemedicine company.

Edited by:

Stacia Woodcock, PharmD

Stacia Woodcock, PharmD, is a pharmacy editor for GoodRx. She earned her Doctor of Pharmacy degree from the University of Kentucky and is licensed in New York and Massachusetts.

Reviewed by:

Rachel Feaster, PharmD, BCOP, BCPS

Rachel Feaster has over 10 years of professional experience in ambulatory, inpatient, pharmacogenomics, and oncology care. She is board certified in oncology and pharmacotherapy.

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References

Cheung, M. C., et al. (2001). Antioxidant supplements block the response of HDL to simvastatin-niacin therapy in patients with coronary artery disease and low HDL. Arteriosclerosis, Thrombosis, and Vascular Biology.

Delgado, B. J., et al. (2023). Estrogen. StatPearls.

View All References (14)

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GoodRx Health has strict sourcing policies and relies on primary sources such as medical organizations, governmental agencies, academic institutions, and peer-reviewed scientific journals. Learn more about how we ensure our content is accurate, thorough, and unbiased by reading our editorial guidelines.

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