There is no such thing as “three major contraindications to taking vitamin C tablets”, vitamin C tablets have a wide range of applications, but those who are allergic to the product are prohibited. Vitamin C tablets are used for the prevention of scurvy, can also be used for a variety of acute and chronic infectious diseases and purpura and other auxiliary treatment. Long-term use of vitamin C tablets, 2-3 grams per day can cause scurvy after stopping the drug, so it is advisable to gradually reduce the amount of stopping the drug. Long-term application of large amounts of vitamin C can cause urate, cysteine salt or oxalate stones. Overdose (daily dosage of more than 1 gram) can cause diarrhea, red and bright skin, headache, frequent urination (daily dosage of more than 600mg), nausea and vomiting, stomach cramps. Excessive application of chewable vitamin C tablets can cause damage to tooth enamel. It is not advisable to overdose on vitamin C tablets for a long period of time, otherwise there is a risk of scurvy symptoms when the drug is suddenly stopped. This product can pass through the placenta and be secreted into breast milk. When taken in excess by pregnant women, it may induce scurvy in newborns. Vitamin C tablets should be used with caution in patients with cysteinuria, gout, hyperoxaluria, oxalate deposition, urate kidney stones, glucose-6-phosphate dehydrogenase deficiency, hemochromatosis, ferrocytic anemia or thalassemia, sickle cell anemia, and diabetes mellitus (due to vitamin C interfering with blood glucose quantification). Vitamin C is a drug, should be used scientifically under the guidance of a doctor, should not be used without authorization.