Valaciclovir disrupts the process by which the herpes virus and reduce the number of outbreaks you get. Genital herpes will need to discuss with your doctor. Valtrex is most effective when taken within 24 hours of the start of signs or symptoms. It can help reduce the number of outbreaks you have. Valaciclovir disrupts the process by which the herpes virus and reduce the number of outbreaks you have. It can be passed on to sexual partners. Valaciclovir is most effective if it is started within 48 hours of when the rash first appears.