Safety and side effects

When taken at suggested doses by mouth, vitamin C supplements are mostly safe. Taking too much vitamin C can cause side effects, including:

• Upset stomach, vomiting and loose stools.
• Heartburn.
• Stomach cramps or bloating.
• Tiredness and sleepiness or not being able to sleep, called insomnia.
• Headache

In some people, oral vitamin C supplements may cause kidney stones. This mainly happens in people who take high doses of the supplements. Long-term use of oral vitamin C supplements over 2,000 milligrams a day raises the risk of serious side effects.

High doses of vitamin C can cause hemolytic anemia in people who have a condition called G6PDH deficiency, which is passed through families.

Before having medical tests, tell your healthcare professional that you take vitamin C supplements. High levels of vitamin C might affect the results of certain tests, such as blood sugar screening tests or stool tests for hidden blood, also called occult blood.