CHEMICAL METHODS of contraception In the 1960s, before the advent of IUDs and oral contraceptives, spermicides (vaginal chemical contraceptives) were used widely. They comprise four categories. a) Foams : foam tablets, foam aerosols b) Creams, jellies and pastes squeezed from a tube c) Suppositories inseed manually, and d) Soluble films - C-film inseed manually. The spermicides contain a base into which a spermicide is incorporated. The commonly used modern spermicides are "surface-active agents" which attach themselves to spermatozoa and inhibit oxygen uptake and kill sperms. The main drawbacks of spermicides are : (a) they have a high failure rate (b) they must be used almost immediately before intercourse and repeated before each sex act (c) they must be introduced into those regions of the vagina where sperms are likely to be deposited, and (d) they may cause mild burning or irritation, besides messiness. The spermicide should be free from potential systemic toxicity. It should not have an inflammatory or carcinogenic effect on the vaginal skin or cervix. No spermicide which is safe to use has yet been found to be really effective in preventing pregnancy when used alone. Therefore, spermicides are not recommended by professional advisers. They are best used in conjunction with barrier methods. Recently there has been some concern about possible teratogenic effects on foetuses, following their use. However, this risk is yet to be confirmed. Ref: Park 25th edition Pgno: 546-547