Benzoic acid occurs naturally in a few plants and is widely used in foods as a preservative, usually as benzoate salts. Supplement sellers sometimes promote it for liver detoxification because the body attaches it to glycine and excretes it as hippuric acid.
The evidence behind those liver claims is thin. What we know comes mainly from food safety data, where small amounts are considered safe.
People who take it as a supplement typically use a capsule or powder with a meal to ease stomach upset. Doses vary a lot because no standard exists.
Watch for allergic reactions and stomach irritation. High doses are toxic. Anyone with kidney problems should skip it, since clearance is slower. Safety during pregnancy or breastfeeding is not known.