about valtrex: "Valtrex is most effective when taken within 24 hours of the start of symptoms. Once daily, whether or not you have symptoms, can reduce the number of outbreaks you get. Some of the most common adverse reactions to the drug are headache, nausea, diarrhea, and vomiting. Valaciclovir disrupts the process by which the herpes virus. Valtrex is also believed to reduce the amount of time for an outbreak if taken soon enough."