OK, so I grabbed Lights Out @ the library on the way home, and it certainly seems to suggest taking 150 mg twice/day. See p. 187 ("150 milligrams of zinc morning and afternoon blocks prolactin . . . [t]ake it with coffee to enhance dopamine, which also blocks prolactin.").
I promise I haven't left out anything relevant in the ellipsis. I suppose you could read it as 150 total, taken between the morning and the afternoon, but seems more like 300 total to me. . .