Valacyclovir works best if it is used within 48 hours after the first symptoms of shingles or genital herpes (e.g., pain, burning, or blisters) begin to appear. Of the two prescription drugs approved by the fda to treat or prevent herpes simplex (hsv) outbreaks (1), acyclovir is more commonly used (2). Valtrex Pdr Acyclovir works by lowering the ability of the herpes virus to multiply in your body. How long does it take for acyclovir to work reddit . But big nasty cold sores that cover half your lip take a whole lot longer than that, abreva or no abreva. This treats the symptoms of your infection. Fluoxetine, sold under the brand names prozac is a selective serotonin reuptake inhibitor (ssri) that may treat headaches, depression, nervousness, restlessness, agitation, anxiety and more. It does take at least 3 full days for it to start to work but the sooner you catch your next one the better.the first one will last a couple of weeks, hopefully less if you started the med so...