It does so by inhibiting the production of an amino acid that humans do not produce. Glyophosate has low to negligible acute toxicity in humans. Most weed-killers are pretty damn toxic to humans so if I had to choose a weedkiller, I would still choose glyphosate. For example, 2,4-D production has to be carefully monitored to minimize dioxin contamination. Agent Orange-related cancers stem from the use of dirty 2,4-D. The low acute toxicity of glyphosate may have given people a false sense of safety while applying it. I remember spraying it on weeds when I was a kid with no protective equipment. With any other weedkiller my father insisted on applying it himself while wearing a mask, heavy gloves etc.
