Coca-Cola douches and contraception

doi:10.1136/bmj.a2873

Published 17 December 2008, doi:10.1136/bmj.a2873
Cite this as: BMJ 2008;337:a2873

Feature

Christmas 2008: Food and Drink

Coca-Cola douches and contraception

Deborah J Anderson, professor of obstetrics/gynaecology and microbiology, lecturer in medicine¹^,2

¹ Boston University School of Medicine, 670 Albany St, Suite 516, Boston, MA 02118, USA, ² Harvard Medical School, Boston, MA 02115, USA

Deborah.Anderson{at}BMC.org

Deborah Anderson explains why women really shouldn’t relyon Coca-Cola for family planning

Coca-Cola douches were a part of folklore about birth controlduring the 1950s and 1960s, before effective contraceptive methodswere readily available.¹ It was rumoured that the acidity ofCoca-Cola killed sperm, and the classic coke bottle provideda convenient "shake and shoot" applicator. Recently, an oldstudy from our group confirming the spermicidal effects of variousCoca-Cola formulations² was awarded the 2008 IgNobel prize inchemistry.³ The press releases surrounding our IgNobel awardmight have repopularised this method, and soft drink douchesare apparently still used to prevent pregnancy in resource-poorsettings.⁴ There are, however, many reason why women shouldnot 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 onlya weak spermicidal effect.⁵

Sperm can out race Coca-Cola

Data from computerised analysis of semen indicate that the forwardvelocity 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. Toimprove efficacy, some Coca-Cola would have to be instilledinto the vagina before ejaculation, but that would undoubtedlybe messy. In addition, as anyone who has ever attempted sexualintercourse in a swimming pool or the sea can testify, excesswatery intravaginal fluid can adversely affect lubrication.Coca-Cola use during intercourse would probably affect the mucinousbiofilm that protects the vaginal epithelium, thereby increasingfriction, trauma, and risk of infection.

Coca-Cola and the vaginal epithelium

As Coca-Cola is said to tenderise steaks and remove corrosionfrom car bumpers,⁷ we tested its effect on human vaginal tissuein vitro using an established toxicology test.⁸ Brief exposureto Coca-Cola visibly damaged the top layer of cells (figure)and decreased transepithelial electrical resistance (TEER),an inverse measure of epithelial barrier permeability (meanTEER after 30 minutes’ exposure to Coca-Cola 380 (SD 87) ${Omega}$ v mean TEER untreated cultures 548 (SD 41) ${Omega}$ , P<0.005). Epithelialdamage and increased permeability could enhance a woman’ssusceptibility to sexually transmitted infections such as HIV/AIDS.⁹

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Scanning electron micrograph of surface of human vaginal tissue exposed in vitro for 30 minutes to tissue culture medium (top) or Coca-Cola (bottom)

Coca-Cola might affect the vaginal flora

Sugar facilitates fungal and bacterial growth, so the high sugarcontent of Coca-Cola could promote vaginal yeast and bacterialinfections. This might be avoided by using Diet Coke, but carbonatedbeverages could have detrimental effects on lactobacilli, beneficialbacteria that colonise the healthy vagina and are essentialfor maintaining the normal vaginal ecosystem.

Douching might promote ascending infections

Douching has been associated with an increased risk of pelvicinflammatory disease and ectopic pregnancy,¹⁰ although it isunclear as to whether this is cause or consequence.¹¹

Unknown teratogenic potential

The Coca-Cola formula is a well guarded secret and is purportedto include "a mix of exotic spices and vegetable extracts fromaround the world." Because of the secrecy, it has not been possiblefor scientists to conduct a systematic study of potential teratogeniceffects of the ingredients.

User failure

Implementation of the Coca-Cola douche requires dexterity andskill and might be unreliable, especially when practised inthe dark. A BMJ article cautioned that misplaced bottle capscan cause serious medical problems.¹²

Better methods are available

The efficacy of the Coca-Cola douche method of birth controlhas 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.¹³Several current contraceptive approaches, including barriermethods (condoms and diaphragms), the intrauterine device, birthcontrol pills, and injectable hormonal methods are significantlymore effective than these methods.¹⁴

The Coca-Cola company states that Coca-Cola is not intendedfor medicinal purposes. Yet, workers in sexual health servicesshould be aware, as the Coca-Cola company continues to use suchsexually charged marketing messages as: "Things go better withCoke," and invites internet literate youngsters to "Discovermore at www.letsgettogether.co.uk."

Cite this as: BMJ 2088;337:a2873

A special thanks to Joseph Politch, Jeffrey Pudney, CaitlinBlaskewicz , Marc Abrahams, and Peter Greenhouse for their encouragementand scientific input.

Competing interests: None declared.

Ethical approval: The original research described was reviewedby the Boston University Medical Campus Human Subject’sInstitutional Review Board and was deemed exempt.

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