Lucy1977 Guaifenesin is the active ingredient in some cough medicines. It works by loosening secretions in the chest when you have a cough, but also loosens any other secretions, for example those in the cervix. In certain parts of cycle the cervical secretions are there to act as a plug so that nasties (can't think of a better word!) can't get in to affect the delicate lining of the womb all ready to accept a fertilised egg. When the secretions are all thin and loose (like at the time around ovulation), they actively help sperm into the right part of the womb for ovulation. This is partly how contraceptive pills work, by thickening this mucous so sperm can't get in. The cough medicine has the opposite effect,a lthough only ones that have Guaifenesin as the active ingredient.
Phew, sorry that was a bit of an essay!