Vitamin C is an essential nutrient in our diet. It has many important roles our body’s immune function, including:

  • wound healing
  • preventing damage to cells
  • building collagen
  • producing chemical messengers called neurotransmitters

Vitamin C can be found in many healthy foods, especially:

  • citrus fruits and juice
  • red and green peppers
  • broccoli
  • strawberries
  • Brussels sprouts

You can also get vitamin C from dietary supplements. Vitamin C supplements are available in many forms:

  • oral tablets
  • chewable tablets
  • extended-release tablets
  • extended-release capsules

Vitamin C is also available by prescription as an injection. The injectable vitamin C can be given into a vein (intravenously), into a muscle (intramuscularly), or under the skin (subcutaneously).

Many people take vitamin C for general health or to boost their immune system. It’s also taken to treat vitamin C deficiency.

Vitamin C deficiency can lead to scurvy. Characteristic symptoms of vitamin C deficiency include:

  • swollen and bleeding gums
  • fatigue
  • poor wound healing
  • joint pain
  • loose teeth
  • colored spots on the skin

In some cases, signs of scurvy can occur within a month of consuming less than 10 milligrams (mg) per day of vitamin C.

Today, scurvy is rare in developed countries. It’s most likely to occur in people who:

  • smoke
  • consume a limited variety of food
  • have nutrient absorption problems

Vitamin C injections are approved by the U.S. Food and Drug Administration (FDA) for treating vitamin C deficiency. They’re also approved for helping to treat serious wounds from trauma or burns.

However, vitamin C injections are typically only used when vitamin C levels need to be increased quickly or when oral supplements can’t be taken due to poor absorption or other reasons.

Off-label use

Vitamin C injections are sometimes used off-label for other conditions, including:

  • cancer
  • general health
  • immune function
  • weight loss

Off-label drug use means that a drug that’s been approved by the FDA for one purpose is used for a different purpose that has not been approved. However, a doctor can still use the drug for that purpose. This is because the FDA regulates the testing and approval of drugs, but not how doctors use drugs to treat their patients. So your doctor can prescribe a drug however they think is best for your care. Learn more about off-label prescription drug use.

Cancer

As early as the 1970s, some researchers were suggesting that using high doses of intravenous vitamin C along with cancer drugs could improve treatment of cancer. Intravenous vitamin C can produce very high levels of vitamin C in the body. Researchers believe that these high vitamin C levels can be toxic to cancer cells without harming the healthy cells of the body.

Some researchers also believe that vitamin C might be able to reduce the side effects of cancer drugs.

However, the potential benefits of intravenous vitamin C in cancer treatment remains controversial. In a systematic review, researchers found inadequate evidence to determine if intravenous vitamin C was beneficial for cancer treatment.

General health and immune function

Some people receive vitamin C injections for general health or to boost immune function and for convenience. The injection means they don’t have to remember to take a supplement pill each day.

It’s true that vitamin C has an important function in the body, but it’s controversial whether taking additional vitamin C — orally or by injection — offers any advantage for people who consume adequate vitamin C in their diet.

The research is inconclusive regarding whether vitamin C reduces the chance of developing cancer, prevents heart disease, prevents eye disease such as macular degeneration, or prevents the common cold.

Weight loss

Vitamin C injection is sometimes used for weight loss. Some research suggests that people who don’t have adequate vitamin C intake aren’t able to burn fat very well.

This means that it’s important to ensure adequate intake of vitamin C. However, there is no scientific research showing that taking vitamin C supplements orally or vitamin C injections causes weight loss.

For treating vitamin C deficiency, the typical vitamin C injection dose is 200 mg once daily for up to a week.

For wound healing, the typical vitamin C injection dose is 1 gram once daily for 5 to 21 days.

For off-label uses, a wide variety of vitamin C injection doses have been used. These typically range from 10 to 100 grams. Doses may be given daily or periodically at different intervals.

Vitamin C injections are safe when used for FDA-approved reasons at typical doses. The most common side effects are pain and swelling at the injection site.

Very high doses of vitamin C injections also seem to have few side effects. Some of these include nausea and pain at injection site. Learn more about vitamin C side effects.

If you’re thinking about getting high doses of vitamin C through injection, talk with your doctor about the potential risks.

Vitamin C increases iron absorption from the food you eat. If you take very high doses of vitamin C, your body might absorb too much iron. This could be a potential problem if you already have high levels of iron in your body.

If you have kidney disease, very high doses of vitamin C might result in kidney damage.

High-dose vitamin C injections might increase your chance of developing a kidney stone. People who’ve had kidney stones in the past may have a greater risk.

When any injection is given, there is also risk for infection.

Vitamin C can interact with some other medications.

Vitamin C can make your urine more acidic. In some cases, this can change how your body gets rid of certain medication. This in turn can change levels of some medications in your body and result in decreased effectiveness or increased side effects. Some of these medications include:

  • fluphenazine (Prolixin)
  • magnesium salicylate (Novasal)
  • mexiletine (Mexitil)
  • salsalate

There is some concern that high-dose vitamin C might make radiation therapy and some chemotherapy drugs less effective. However, this is controversial, and more evidence is needed.

If you’re taking other medications or being treated for cancer, talk with your doctor before taking high-dose vitamin C injections.

Vitamin C injections are typically only used for correcting a vitamin C deficiency when oral supplements can’t be taken.

High-dose vitamin C injections are used for off-label conditions, especially cancer. Some researchers think that vitamin C injections can make chemotherapy work better or prevent some chemotherapy side effects. There is some research that suggests vitamin C injections might help reduce side effects and improve quality of life. More research is needed to determine if vitamin C can help fight cancer.

Some people use vitamin C injections for weight loss. However, there’s no scientific support for this use.

Talk with your doctor before using vitamin C injections.