If you think that using a soft drink douche is good means of birth control, you may want to buy cases of diapers. This old urban legend is bunk, according to Harvard Medical School's Deboran Anderson and can harm a woman doing it.
The professor in obstetrics and gynaecology says that the douches were used during the 1950's and 1960's. It was believed that the acidity of the soft drink would kill sperm. In some poorer countries the practice is still going on as a post-coital means of birth control.
These methods have shown no evidence of working but there are fears that they can cause harm. Coca-Cola damages the top layers of cells in the vagina making a woman more susceptible to sexually transmitted disease. Even though it does not harm the sperm that the douche is being used to kill it does remove the healthy bacteria in the vagina which is a risk factor for bacterial and fungal infections.