Why Does Pep Fail? – Does Pep Work after 72 Hours Does Pep Work after 72 Hours ? How well does PEP work? If taken within 72 hours after possible exposure, PEP is highly effective in preventing HIV. But to be safe, you should take other actions to protect your partners while you are taking PEP. … Continue reading Why Does Pep Fail? – Does Pep Work after 72 Hours