Vitamin C – Oral Vs. High Dose

Patients often inquire about vitamin C therapy and ask if we offer “High Dose Vitamin C.” This can mean different things to different people, and has led to some confusion, regarding oxidant/anti-oxidant properties. Below is some information regarding different types of Vitamin C therapies, namely oral and intravenous, to help clarify these treatments.

Oral supplementation of vitamin C:

Vitamin-C is one of the most well-known vitamins.  Orally the gut can absorb up to 1,000 mg per hour.  It is irritating to the digestive tract and can cause diarrhea when intake is more than the body can use so most people have to increase their daily dose slowly over time.  Ask your doctor about how to comfortably achieve optimal oral doses of vitamin C daily intake.

Intravenous (IV) vitamin C infusions:

Vitamin-C can be infused into the blood stream in much higher doses than can be achieved taken by mouth.  This route does not cause diarrhea or digestive tract irritation.  Vitamin C, at doses lower than 15-25 grams (15,000-25,000 mg) depending on the individual, is a potent antioxidant (scavenger of free radicals) that can boost the immune system, fight infection and improve quality of life.

High Dose Intravenous Vitamin C infusions:

These infusions usually start at 25 grams and can increase to 100 grams, depending on the individual’s needs and test results.  This elevated dose strength allows the concentration in the body to reach a peak plasma level (saturation) at which point the action of the vitamin C is now PRO-oxidative, meaning it generates free radicals.  It interacts with iron and copper to create hydrogen peroxide which is used to kill pathogenic bacteria and cancer cells.  Hydrogen peroxide is also created by our immune system and is perfectly safe in this instance.

Upper Tolerable Limit of Vitamin C:

Vitamin C is incredibly safe at very high levels.  While the diarrhea and gastrointestinal discomfort that can occur with high levels of oral ingestion is not pleasant, it is not permanently damaging or life threatening.  You would have to take over 755,000 mg (755gm) in one short period of time to experience life threatening reactions and this is absolutely not possible, even with IV dosing.


G-6-PD is Glucose-6-Phosphate-Dehydrogenase and is an enzyme responsible with breaking down excess carbohydrates in the cell, mostly in red blood cells.  It is necessary to test for adequate levels before administering high dose IV vitamin C treatments because a deficiency in this enzyme can cause hemolytic anemia (breaking open and death of red blood cells).  It is estimated that 5-15% of the population has a genetic anomaly that leads to decreased amounts of this enzyme available.  These people can still receive high dose vitamin C but on a modified schedule, with frequent blood testing and other supportive measures.

Further Reading:

Here are a couple of journal articles demonstrating the safety of vitamin C and the difference between oral and intravenous, in case you are interested.  The first documentation of vitamin C as a cancer treatment was in 1949.  There have been numerous volumes of research on this wonderful vitamin and it continues to be studied for treatment of various cancers and other illnesses.  Vitamin C is safe to use with chemotherapy and radiation.  It has not been demonstrated that it will decrease effectiveness of chemotherapy or radiation.

Vitamin C Pharmacokinetics: Implications for Oral and Intravenous Use

Pharmacokinetics of Vitamin C: insights into the oral and intravenous administration of ascorbate