Nonoxynol-9 is an ingredient found in many different spermicides, such as commercial contraceptive foams, diaphragm jellies and the solutions used to lubricate certain brands of condoms. As a spermicide, N-9 or Nonoxynol-9 attacks the acrosomal membranes of the sperm, causing the sperm to be immobilized

Nonoxynol-9 is mostly effective at preventing pregnancies, with a failure rate somewhere between 10 and 20 percent; however, the organic compound offers no protection against HIV or other sexually transmitted diseases. In 2007, the FDA began requiring products containing nonoxynol-9 to carry warning labels to this effect.

Despite its use in condom lubricating solutions, nonoxynol-9 is not an effective personal lubricant. The compound has an irritating effect on vaginal and rectal tissues.