Narrator: This is Science Today. The state of California may become the first large state to issue guidelines for doctors about prescribing a little-known 'morning after' drug treatment for HIV exposure. Dr. Michelle Roland of the University of California, San Francisco has been studying the treatment called post-exposure prophylaxis, or PEP, since 1997.

Roland: So post-exposure prophylaxis generally refers to a 28-day course of two to three anti-HIV drugs that are taken within 72 hours of an exposure. This has been used in the healthcare worker setting following needle-sticks for many years.

Narrator: Roland says there's no guarantee that the treatment will work, but results from animal and human studies point in the direction that it should.

Roland: We very first started thinking about the use of PEP following non-occupational exposures when a study was published in 1996 that demonstrated that PEP was effective in health care workers and it reduced their risk of getting HIV by about 80 percent.

Narrator: For Science Today, I'm Larissa Branin.