Spermicides work by forming a chemical barrier that either kills sperm or paralyzes them. So the sperm can't pass through your cervix to fertilize the egg. Spermicides can be used alone as a form of contraception, but they are much more effective when used with another type. Some types of contraception work best with certain types of spermicide. Diaphragms work best with contraceptive creams or jellies that are labeled for use with diaphragms.
Male condoms work best when the women uses contraceptive foams, films, or inserts.
No prescription is needed. Spermicide alone is one of the less effective forms of contraception against pregnancy. When used with other forms of contraception such as condoms, the protection against pregnancy increases a good deal. It's obvious that spermicide is most effective against pregnancy when it is used all the time and always used correctly. It is best to use condoms for STD and HIV protection.