Approximate effectiveness: not too good- the failure rate of spermicide alone is very high - estimates range from 5 to 59% at Epigee.org!
The American Pregnancy Association site states a failure rate when used properly of 8%, but when used by most people, spermicide has a failure rate around 26%
Little or no protection against most STDs. May be used with condoms to improve the rate of pregnancy prevention of the condom.
Some research questions the effectiveness of spermicide, saying it makes no difference to pregnancy rates compared to a condom without spermicide. it's your choice. Spermicides are inserted into the vagina to help kill sperm. They come in various forms and their effectiveness may not be the same in all the forms. Spermicides can be in the form of a jelly, foam, cream, tablets or suppositories. A suppository looks sort of like a large pill and it gets inserted into the vagina where it dissolves.
The different types are used in different ways and at different times so read the instructions very carefully. Then read them again! Spermicides kill the sperm that enters the vagina and some may present a barrier to the cervix. Spermicides don't last that long so a couple may have to apply more spermicide if they are going to have sexual intercourse within a certain time after the spermicide is first applied, and before each time they have sex, even if it is within the time listed in the manufacturer's instructions.
Spermicides can be messy and are not that effective at birth control, and in a few people can irritate the penis or vagina.
They are available at pharmacies and clinics and are fairly low priced. No prescription or parental consent is needed. Epigee.org states that a previously perceived slight improvement in STD infection rates with spermicide was not true. As well, spermicide may cause an allergic reaction in some people and urinary tract infections in some women. So while it used to be thought that spermicides might give a bit of protection against Gonorrhea, PID (Pelvic Inflammatory Disease), and some vaginal infections, they should not be considered as STD protection at all. More recent research shows that, while that may be true in a laboratory, in real life, it seems like it does not. As well, the common spermicide nonoxyol-9 , or "N-9" can irritate, even strip the lining of the vagina or rectum, possibly making that person more susceptible to an STD. Contracept.org/spermicides (link no longer active) says N-9 can even lead to other STDs due to its damaging cervical cells.