Verywell Health explains that vitamin C supplements can reduce the concentration of fluphenazine (an antipsychotic drug) in the blood, rendering the medication less effective. They may have the same effect on chemotherapy drugs. According to HealthlineVitamin C can increase your urine acidity, leading to increased excretion of certain drugs. This can result in decreased effectiveness.
The NIHIt is noted that most people have enough vitamin C to go around and that supplements are unnecessary. However, vitamin C supplements can be prescribed to people who have difficulty absorbing it. If this is you, then please consult your doctor. National Library of MedicineDiscuss your medication and any possible supplements with your doctor. This will allow your doctor to monitor you closely, give you advice on side effects and even modify your prescription if necessary. According to the NIH, consulting a doctor before taking vitamin C supplements is especially important for people being treated for cancer.