About 500,000 American women are thought to use vaginal spermicidal products containing nonoxynol-9 for contraception, but data on the effectiveness of these agents are limited. Raymond and colleagues studied the effectiveness and safety of five products (three gels, a film, and a suppository) containing from 52.5 to 150 mg of nonoxynol-9.

The researchers enrolled more than 1,500 women 18 to 40 years of age at 14 U.S. sites. Participants were required to be healthy and to have a low risk of sexually transmitted diseases and no evidence of subfecundity. Each woman and her partner were required to consent to a moderate risk of pregnancy during the study. Following an intake assessment that included physical examination, Papanicolaou smear, and screening for pregnancy, women were assigned randomly to one of the five products. The women agreed to rely on this product for contraception during the study and were instructed in back-up emergency contraception.

Participants were asked to record use of contraception, occurrences of intercourse, and menstrual history in a symptom diary. All participants were reassessed at four, 17, and 30 weeks after entry to the study. Pregnancy testing was performed at each visit, and a full pelvic examination was performed and a wet preparation was obtained at the final visit. Quizzes were used at intake and at the four-week visit to assess understanding of contraception, and use of spermicide and emergency contraception. At the four-week and final visits, questionnaires about the acceptability of the spermicide were completed. Home pregnancy tests were used by the patients at two, 10, and 23 weeks.

The groups were comparable in baseline characteristics on entry to the study. The median age was 26 years, and the median frequency of intercourse in the previous four weeks was twice weekly. About 60 percent of the women relied on the spermicide for six months or became pregnant earlier. Between 7 and 17 percent of the women in each group became pregnant while using the spermicide. Between 15 and 17 percent of each group discontinued use of the spermicide early, and 22 percent were lost to follow-up. The cumulative probability of pregnancy during six months of typical use ranged from 10 to 22 percent. In the three groups using 100 mg of nonoxynol-9 in gel, film, or suppository forms, the probability ranged from 10 to 16 percent. The probability rose to 22 percent in the group using the gel containing 52.5 mg of the spermicide, and to 14 percent in the group using the 150 mg gel. Emergency contraception was used 109 times during the study. Very few side effects were reported, and the frequency of monitored or reported adverse effects was similar between groups.

The authors conclude that spermicidal products are generally safe but are associated with higher pregnancy rates than other forms of contraception. Patients using preparations with the highest amounts of non-oxynol-9 had the lowest pregnancy rates.