Coca-Cola douches and contraceptionBMJ 2008; 337 doi: http://dx.doi.org/10.1136/bmj.a2873 (Published 18 December 2008) Cite this as: BMJ 2008;337:a2873
- 1Boston University School of Medicine, 670 Albany St, Suite 516, Boston, MA 02118, USA
- 2Harvard Medical School, Boston, MA 02115, USA
Coca-Cola douches were a part of folklore about birth control during the 1950s and 1960s, before effective contraceptive methods were readily available.1 It was rumoured that the acidity of Coca-Cola killed sperm, and the classic coke bottle provided a convenient “shake and shoot” applicator. Recently, an old study from our group confirming the spermicidal effects of various Coca-Cola formulations2 was awarded the 2008 IgNobel prize in chemistry.3 The press releases surrounding our IgNobel award might have repopularised this method, and soft drink douches are apparently still used to prevent pregnancy in resource-poor settings.4 There are, however, many reason why women should not rely on this method.
Coca-Cola is not a strong spermicide
In our study we mixed Coca-Cola with human semen (5:1 ratio) and reported that sperm were immobilised within one minute. A subsequent toxicology study found that Coca-Cola has only a weak spermicidal effect.5
Sperm can out race Coca-Cola
Data from computerised analysis of semen indicate that the forward velocity of human spermatozoa can exceed 18 cm/hour.6 Therefore, a well placed sperm can reach the cervical canal within seconds, thus escaping the effect of postcoital douching solution. To improve efficacy, some Coca-Cola would have to be instilled into the vagina before ejaculation, but that would undoubtedly be messy. In addition, as anyone who has ever attempted sexual intercourse in a swimming pool or the sea can testify, excess watery intravaginal fluid can adversely affect lubrication. Coca-Cola use during intercourse would probably affect the mucinous biofilm that protects the vaginal epithelium, thereby increasing friction, trauma, and risk of infection.
Coca-Cola and the vaginal epithelium
As Coca-Cola is said to tenderise steaks and remove corrosion from car bumpers,7 we tested its effect on human vaginal tissue in vitro using an established toxicology test.8 Brief exposure to Coca-Cola visibly damaged the top layer of cells (figure) and decreased transepithelial electrical resistance (TEER), an inverse measure of epithelial barrier permeability (mean TEER after 30 minutes’ exposure to Coca-Cola 380 (SD 87) Ω v mean TEER untreated cultures 548 (SD 41) Ω, P<0.005).⇓ Epithelial damage and increased permeability could enhance a woman’s susceptibility to sexually transmitted infections such as HIV/AIDS.9
Coca-Cola might affect the vaginal flora
Sugar facilitates fungal and bacterial growth, so the high sugar content of Coca-Cola could promote vaginal yeast and bacterial infections. This might be avoided by using Diet Coke, but carbonated beverages could have detrimental effects on lactobacilli, beneficial bacteria that colonise the healthy vagina and are essential for maintaining the normal vaginal ecosystem.
Douching might promote ascending infections
Unknown teratogenic potential
The Coca-Cola formula is a well guarded secret and is purported to include “a mix of exotic spices and vegetable extracts from around the world.” Because of the secrecy, it has not been possible for scientists to conduct a systematic study of potential teratogenic effects of the ingredients.
Implementation of the Coca-Cola douche requires dexterity and skill and might be unreliable, especially when practised in the dark. A BMJ article cautioned that misplaced bottle caps can cause serious medical problems.12
Better methods are available
The efficacy of the Coca-Cola douche method of birth control has never been tested in a placebo controlled clinical trial, and probably never will be. Early epidemiological studies, however, reported that postcoital douching was no more effective than “rhythm” or “penile withdrawal” methods, which are unreliable.13 Several current contraceptive approaches, including barrier methods (condoms and diaphragms), the intrauterine device, birth control pills, and injectable hormonal methods are significantly more effective than these methods.14
The Coca-Cola company states that Coca-Cola is not intended for medicinal purposes. Yet, workers in sexual health services should be aware, as the Coca-Cola company continues to use such sexually charged marketing messages as: “Things go better with Coke,” and invites internet literate youngsters to “Discover more at www.letsgettogether.co.uk.”
Cite this as: BMJ 2088;337:a2873
A special thanks to Joseph Politch, Jeffrey Pudney, Caitlin Blaskewicz , Marc Abrahams, and Peter Greenhouse for their encouragement and scientific input.
Competing interests: None declared.
Ethical approval: The original research described was reviewed by the Boston University Medical Campus Human Subject’s Institutional Review Board and was deemed exempt.