Valtrex (Valacyclovir) and Cold Sores

Herpes labialis (also called cold sores or fever blisters) is usually caused by herpes simplex virus 1 (HSV-1). Cold sores usually form on the lips or skin around the mouth, nose and on the chin.

Valtrex (valacyclovir) is indicated for the treatment of cold sores in adults and children age 12 and older. It reduces the episode duration and time to lesion healing by 20% (1.1 to 1.3 days)1. Early treatment with Valtrex also prevents the development of vesicles and crusts.

Valtrex is helpful in preventing recurrent cold sores. Two studies showed that once-daily 500 mg of valacyclovir for 4 months increased the time interval until the next outbreak from 9.6 to 13.1 weeks2. During the 4-month period, 60% of the patients in the valacyclovir group were outbreak-free compared with 38% in the placebo group.

Valtrex dosage for cold sores: 2 grams twice a day for 1 day, taken about 12 hours apart. The treatment should be initiated at the earliest symptoms of a cold sore (e.g., tingling, itching, or burning).

How long to take Valtrex for a cold sore? It should not be taken for more than 1 day for an acute episode.

When Valtrex is most effective?

HSV-1 replication (that triggers cold sores) occurs rapidly and during a brief period3.

Treatment should be started as early as possible after first signs of cold sores, because viral replication is most active in the prodromal period or within the first 8 hours after lesion onset. The maximum number of herpes lesions occurs in the first 48 hours.

Therefore the window of opportunity for Valtrex to provide a benefit is during the early and brief period of time right after first signs of cold sores.

See also


  • 1. Spruance SL, Jones TM, Blatter MM. et al. High-dose, short-duration, early valacyclovir therapy for episodic treatment of cold sores: results of two randomized, placebo-controlled, multicenter studies. Antimicrob Agents Chemother. 2003 Mar;47(3):1072-80. PubMed
  • 2. Baker D, Eisen D. Valacyclovir for prevention of recurrent herpes labialis. Cutis. 2003 Mar;71(3):239-42.
  • 3. Spruance SL, Green JA, Chiu G, Yeh TJ, Wenerstrom G, Overall JC Jr. Pathogenesis of herpes simplex labialis: correlation of vesicle fluid interferon with lesion age and virus titer. Infect Immun. 1982 Jun;36(3):907-10.

Author: OriginalDrugs Team
Last reviewed: February, 2015

Quick facts

valtrex for oral herpes
  • Valacyclovir may help prevent cold sore outbreak if taken during a prodromal stage.
  • Most cold sore lesions progress from the vesicle stage to the ulcer or soft crust stage within 48 hours, with a hard crust forming by day 2 or 3.
  • One day and even a single dose of antiviral medication may speed the healing of herpes labialis lesions by up to 2 days.