Spermicides kill sperm, stopping them from swimming to an egg and starting a pregnancy. They come in different forms, but all have the chemical nonoxynol-9, which kills sperm. Spermicides come in suppositories, foams, creams, inserts, film and gels. You can use a spermicide alone, but it�s better at preventing pregnancy when used with a condom or diaphragm.

Spermicides are inserted into the vagina before intercourse.  With some products, like film, inserts and suppositories, you have to wait a little while -- usually 15 to 30 minutes -- before having intercourse, while the warmth of your body melts the spermicide. Foams, creams, and gels are effective as soon as they are inserted.

When used alone, spermicides prevent pregnancy about 94 percent of the time, if used perfectly, every single time you have sex. With more typical use -- mistakes and all -- spermicides prevent pregnancy about 70 to 75 percent of the time. Add a condom and you�ve just given yourself double protection, against both pregnancy and disease. The two together prevent pregnancy 97 percent of the time -- a much safer rate.

Burning and itching in the vulva, vagina and the skin of the genitals are the most common side effects, although this doesn�t happen to everyone. Some women say using spermicides increases their vaginal discharge after sexual intercourse.

Spermicides are sold in many drug stores and pharmacies, as well as online and in family planning clinics. One tube of gel or cream typically costs about $8 to $10. One dose of an insert, film or foam typically costs about $1 and is sold in packs of 3, 6 or more.