The rumor that Coca-Cola can be used as a douche has been around since the 1950s. Although sperm is alkaline and cola is acidic, this is not recommended, in fact it’s even dangerous. Any kind of douching is unhealthy. The vaginal environment naturally flushes out the system on a regular basis. Douching only upsets the natural balance of the chemical environment within the vagina, thus increasing the likihood of infections such as PID (Pelvic Inflammatory Disease). The vaginal environment is naturally acidic during the non-fertile phase of the menstrual cycle, thus creating its own spermicide. During the fertile phase (ovulation) vaginal fluid changes viscosity; it becomes whitish, thicker, and stringy in order to facilitate sperm mobility. The pH level also under goes a change; it becomes more alkaline (i.e. hospitable to sperm). Cola only dilutes ejaculate (in lab conditions) but doesn’t kill the sperm. Besides, by the time you reach for the bottle, sperm has already traveled through the cervical os and is well out of reach of any spermicide. That is why spermicide is applied only before intercourse.
Alternative forms of birth control would be the natural methods such as the Basal Body Temperature (BBT) and the Cervical Mucus Method. A lesser known male birth control method is Male Multiple Orgasm, which is non-ejaculatory. It’s always best to use multiple forms of birth control, since no known birth control method is 100% effective.
Sources: Center for Disease Control and Prevention website, PID facts, http://www.cdcnpin.org/stdawareness/the-facts/english/06_PID_revd.pdf
Chica, M, The Multi-Orgasmic Man, HarperOne, New York, 1997
Douching Fact Sheet, http://womenshealth.gov/publications/our-publications/fact-sheet/douching.cfm