I agree with stinky on this one guys, I have seen no scientific proof beyond anecdotal posts on forums saying to use birth control pills or using piss from a pregnant horse or from a pregnant woman.
There is no Science behind this that I am aware of, if you have a scientific report that I would read and study. But until then I would take caution. Sex is not determined in the seed DNA but rather in the RNA so that means that the true sex of the plant is not determined until between the third and forth week of true veg. That is why environment is so important at that time of the cycle of life of this plant.
If you go cheap you grow cheap. - Me