Any vaginal spermicide (suppository, film, cream, jelly, etc) is very helpful at preventing pregnancy, although it will not reduce your chances of getting STDs. As with any method of birth control, the more carefully and consistently it is used the better it functions at preventing pregnancy. Vaginal spermicides alone are about 80% effective (20 pregnancies per 100 couples per year) because they are usually used sporadically. However, if vaginal spermicides are used properly 100% of the time, and are combined with a condom 100% of the time, the risk of pregnancy can be as low as 6 in 10,000 chances per year! And, of course, it is recommended anyway that you use a condom every time you have sex because it protects against STD transmission as well as pregnancy.