Acidification of the urine by ascorbic acid may cause precipitation of cysteine, urate, or oxalate stones and will alter the excretion of certain other drugs administered concurrently.
Concurrent use of large doses vitamin C and warfarin may interfere with the anticoagulant effect.
Concurrent administration of ascorbic acid and disulfiram will interfere with the effectiveness of disulfiram given to patients to encourage abstention from alcohol.
Concurrent administration of ascorbic acid and bishydroxycoumarin may influence the intensity and duration of action of bishydroxycoumarin.
Diabetic patients taking more than 500 mg/day ascorbic acid may obtain false readings of their urinary glucose test.