Lethal dose of sodium fluoride is about 5 grams. Do not, from this, attempt to figure out how much mouthwash you can drink. However, chlorine is also a reactive, elemental gas (and a halogen, as is fluorine, although flourine often does not react in the typical halogen way) That said, sodium chloride is table salt. But I can't help thinking that if mouthwash was killing people then we would be seeing commercials on TV from lawyers offering to sue the company that makes listerine.