What should you never mix with vitamin C?

What should you never mix with vitamin C? Vitamin C should not be mixed with certain substances due to interactions reducing effectiveness or causing adverse effects. Do not mix vitamin C with vitamin B12 in same supplement at high doses, as vitamin C may degrade B12. Avoid mixing vitamin C supplements with aluminum-containing antacids, as vitamin C may increase aluminum absorption. Do not mix with certain chemotherapy drugs without doctor guidance, as high dose antioxidants may interfere. Avoid mixing high dose vitamin C with iron supplements unless doctor advises, as it increases iron absorption which may be harmful in iron overload conditions. Do not mix topical vitamin C with benzoyl peroxide, retinol, and AHAs simultaneously without layering correctly, as combination may cause irritation or reduce effectiveness, though can be used at different times. Also avoid mixing vitamin C with copper, as it may cause oxidation. For medications, vitamin C may interact with warfarin, statins, and aspirin, so consult doctor before high doses. So never mix with certain antacids, chemotherapy, and be cautious with skin care actives and iron without medical advice.