What medication cannot be taken with vitamin C?

According to CDC data from 2017–2018, over 57% of U.S. adults used a dietary supplement in the past 30 days [1.9.1]. While Vitamin C is common, many don't know the answer to, 'What medication cannot be taken with vitamin C?'

Quick Summary

Vitamin C supplements can interfere with various prescription and over-the-counter drugs, altering their effectiveness or increasing side effects. Key interactions involve chemotherapy, statins, blood thinners, and antacids.

Key Points

• Blood Thinners: High-dose vitamin C can make anticoagulants like warfarin less effective, increasing clot risk [1.2.4].

• Chemotherapy: Vitamin C, as an antioxidant, might protect cancer cells and reduce the effectiveness of chemotherapy treatments [1.2.2].

• Statins and Niacin: The combination may be less effective at improving 'good' HDL cholesterol levels when taken with vitamin C [1.2.1].

• Aluminum Antacids: Vitamin C increases aluminum absorption, posing a toxicity risk for those with kidney disease [1.6.3].

• ADHD Medication: Vitamin C can decrease the absorption of amphetamine-based drugs like Adderall, making them less potent [1.5.3].

• Estrogen: Taking vitamin C with estrogen-based drugs (like birth control) can elevate estrogen levels and side effects [1.7.4].

• Professional Consultation is Crucial: Always inform your doctor about any supplements you take to avoid potentially harmful interactions [1.4.1].

Understanding Vitamin C and Its Role

Vitamin C, or ascorbic acid, is a vital nutrient your body needs for many functions. It is a powerful antioxidant, helps in collagen formation, aids in iron absorption, and supports the immune system [1.4.1, 1.10.5]. While most people get enough vitamin C from a balanced diet rich in fruits and vegetables, many turn to supplements. A 2021 CDC report noted that dietary supplement use increases with age, with over 80% of women aged 60 and over reporting use [1.9.1]. However, even though it's a natural vitamin, high-dose vitamin C supplements can interact with numerous medications, potentially leading to reduced efficacy or increased risk of side effects [1.2.1]. It is crucial to consult a healthcare provider before starting any new supplement, including vitamin C [1.4.1].

Medications with Reduced Effectiveness

Taking high doses of vitamin C can make certain medications less effective. This can have serious health consequences, from increasing the risk of blood clots to rendering life-saving treatments less potent [1.2.1, 1.2.2].

• Blood Thinners (Anticoagulants): High doses of vitamin C (1 gram or more) may reduce the effectiveness of blood thinners like warfarin (Jantoven) [1.2.1, 1.4.3]. This interference can increase the risk of developing a blood clot [1.2.1].
• Statins and Niacin: These medications are used to manage high cholesterol. Some studies suggest that taking vitamin C with a combination of statins and niacin could reduce the medication's ability to raise HDL ("good") cholesterol [1.2.1, 1.4.3].
• Chemotherapy Drugs: As an antioxidant, vitamin C might protect cancer cells from the effects of chemotherapy, potentially making the treatment less effective [1.2.2, 1.4.1]. This is a significant concern, and patients undergoing cancer treatment should always consult their oncologist before taking any supplements [1.2.3].
• Amphetamine-based ADHD Medications: Vitamin C can decrease the absorption and increase the excretion of amphetamine-based medications like Adderall [1.5.3, 1.5.4]. This occurs because vitamin C acidifies the gastrointestinal tract and urine, which makes the typically alkaline Adderall less bioavailable [1.5.3, 1.5.4]. To avoid this interaction, it is often recommended to take vitamin C supplements and amphetamine-based drugs at least one to two hours apart [1.5.3, 1.6.4].
• Antiviral Protease Inhibitors: For individuals undergoing treatment for HIV with protease inhibitors like indinavir (Crixivan), vitamin C can lower the drug's concentration in the body, reducing its effectiveness and increasing the risk of the virus developing resistance [1.2.1, 1.8.2]. A study showed that 1000 mg of vitamin C daily significantly reduced indinavir concentrations [1.8.1].

Medications with Increased Side Effects or Toxicity

In other cases, vitamin C can enhance the absorption or effects of certain medications, leading to a higher risk of side effects or toxicity.

• Aluminum-Containing Antacids: Vitamin C significantly increases the absorption of aluminum from medications like Mylanta or Gaviscon [1.2.3, 1.6.4]. For most people, this is not a major concern. However, for individuals with kidney problems, this can lead to a dangerous buildup of aluminum, causing issues like confusion, weakness, and seizures [1.2.1, 1.6.5]. It's recommended to take vitamin C two hours before or four hours after these antacids [1.6.4].
• Estrogen-Containing Medications: Taking vitamin C with oral contraceptives or hormone replacement therapy may increase estrogen levels [1.7.4]. Vitamin C may interfere with how the body metabolizes estrogen [1.7.1, 1.7.3]. Elevated estrogen levels can lead to side effects such as mood swings and an increased risk of blood clots and certain hormone-sensitive cancers [1.7.1].
• Levothyroxine: Vitamin C may increase the absorption of levothyroxine, a medication used to treat thyroid disorders. This could potentially lead to increased effects and side effects of the thyroid medication [1.2.4].

Comparison of Vitamin C Drug Interactions

Medication Class	Interaction with Vitamin C	Potential Consequence	Management Strategy
Blood Thinners (e.g., Warfarin)	Decreases medication effectiveness [1.4.3]	Increased risk of blood clots [1.2.1]	Consult doctor; regular blood monitoring is crucial [1.2.4].
Statins & Niacin	May reduce the effect on HDL cholesterol [1.2.1]	Ineffective cholesterol management [1.2.2]	Discuss with doctor; monitor cholesterol levels [1.4.1].
Chemotherapy Agents	May reduce treatment efficacy [1.2.2]	Impaired cancer treatment [1.2.3]	Avoid without oncologist's approval [1.4.2].
Aluminum-Containing Antacids	Increases aluminum absorption [1.6.3]	Aluminum toxicity, especially with kidney issues [1.6.5]	Separate doses by at least 2-4 hours [1.6.4].
Estrogen-Based Drugs	Increases estrogen levels [1.7.4]	Increased risk of side effects like blood clots [1.7.1]	Consult a healthcare provider before combining [1.7.1].
Amphetamines (e.g., Adderall)	Decreases medication absorption [1.5.4]	Reduced effectiveness for ADHD symptoms [1.5.1]	Take vitamin C at least one hour apart from medication [1.5.3].
Protease Inhibitors (e.g., Indinavir)	Decreases medication effectiveness [1.8.2]	Ineffective HIV treatment, risk of resistance [1.2.1]	Avoid combination; consult with your doctor [1.2.3].

Conclusion: Prioritize Safety and Professional Guidance

While vitamin C is an essential nutrient, its supplementation is not without risks, especially for individuals taking certain medications. Interactions can range from mildly reducing a drug's effectiveness to causing severe toxicity. The key takeaway is that "natural" does not always mean "safe" when combined with pharmaceuticals. Always maintain an open dialogue with your healthcare provider or pharmacist about all supplements you are taking, including vitamin C. They can provide personalized advice based on your health status and medication regimen to prevent harmful interactions and ensure your treatments remain effective and safe.

For more information on supplement safety, you can visit the National Institutes of Health (NIH) Office of Dietary Supplements.

Frequently Asked Questions

Can I take vitamin C with blood pressure medication?

Some studies suggest vitamin C might have a modest effect on blood pressure, but there is no strong evidence of a major interaction with beta-blockers. However, it's always best to consult your healthcare provider [1.4.5].

How long after taking medication can I take vitamin C?

For medications like aluminum-containing antacids or Adderall, it is recommended to space them out. A general guideline is to take vitamin C at least two hours before or four hours after antacids [1.6.4], and at least one hour apart from Adderall [1.5.3].

Does vitamin C affect antibiotics?

Yes, vitamin C can interact with some antibiotics. For example, it may increase the blood levels of tetracycline antibiotics (like doxycycline and minocycline) while decreasing the effectiveness of vitamin C itself [1.2.5].

Is it safe to take 1000mg of vitamin C daily?

While many supplements contain 1000mg, this high dose can interact with several medications, including warfarin and protease inhibitors [1.2.1, 1.8.1]. The tolerable upper intake level is 2,000 mg per day for adults; exceeding this increases the risk of side effects like digestive upset and kidney stones [1.10.1, 1.10.2].

Can taking vitamin C with NSAIDs like ibuprofen cause problems?

Combining large doses of vitamin C with nonsteroidal anti-inflammatory drugs (NSAIDs) like ibuprofen or aspirin may increase the risk of kidney problems, especially with long-term use. Additionally, NSAIDs can increase the amount of vitamin C your body excretes [1.2.1, 1.2.3].

Does vitamin C interact with medications for diabetes?

Yes, vitamin C supplements have been shown to lower blood sugar levels, which could affect the dosage needs for medications like metformin or insulin. High doses can also interfere with certain blood sugar monitoring devices, causing falsely elevated readings [1.2.3].

Why does vitamin C interact with so many drugs?

Vitamin C can alter the way drugs are absorbed, metabolized, or excreted. For example, it can change the acidity of the stomach and urine, affecting drug absorption [1.5.3], or it can interfere with enzymes that break down medications, like those in the P-450 system [1.8.1].