One of the most heavily trafficked entries on this site is that on TBHQ. While it’s an antioxidant, it’s a synthetic one, and some have suggested it might be toxic. Another antioxidant, ferulic acid, found in wheat, works on much the same principle and has found less blame.
Hydroquinone is, too, an antioxidant, but it exhibits some toxicity and potential carcenogenicity. The lesson that all “polyphenols” are not medicines and all “chemical antioxidants” are not toxins is well taken. The dose, the structure, and (perhaps most importantly) the metabolism make the poison.