Studies have not produced definitive data on the efficacy of spermicides used alone (without a diaphragm or cervical cap) but research suggests the failure rate for typical users may be in the range of 20% per year.
Some spermicide products require the couple to wait 10 minutes or more after inserting the spermicide before having sex. One dose of spermicide is usually effective for one hour. For repeated intercourse, additional spermicide must be applied. And after intercourse, the spermicide has to remain in place for at least six to eight hours to ensure that all sperm are killed. The woman should not douche or rinse the vagina during this time.