Valtrex is for the treatment of genital herpes, cold sores, and shingles. Valtrex is most effective within the first three days and before symptoms have appeared. Even if you are taking Valtrex to reduce the risk of spreading genital herpes, you should not engage in sexual intercourse during an outbreak of lesions. You should continue to use condoms as protection against transmitting genital herpes. People who are allergic to acyclovir or valacyclovir and people with immunodeficiency disorders, such as AIDS, should inform their doctors of these facts before taking Valtrex.