How does PEP work?

It takes a few days for HIV to become established in the body following exposure. PEP drugs given at this time may help the body’s immune system to stop the virus from replicating (multiplying) in the infected cells of the body. The cells originally infected would then die naturally within a short period of time without producing more copies of HIV.

But if the HIV virus is already in the body, isn’t it too late?

Not if you act quickly. After HIV gets in the bloodstream it takes some time before it permanently establishes itself in the body. If a person who has been exposed to HIV acts quickly to get PEP (within 72 hours) they stand a good chance of stopping the virus from establishing itself in their body.

So, if I take PEP I won’t become HIV positive?

Research indicates that taking PEP makes infection with HIV a lot less likely. But PEP doesn’t work every time – some people who take it still end up with HIV afterwards. It can fail because:

  • the person doesn’t or isn’t able to take PEP as prescribed (every day for a month)
  • some anti-HIV drugs don’t work against some strains of HIV (although this is rare)
  • the initial viral load (the amount of HIV) in the body was too great for the drugs to be effective

However, the sooner PEP treatment is begun after exposure to the virus, the more likely it is to work.