Conclusive proof is lacking, but many people report over-the-counter, inexpensive lysine pills help treat cold sores. The body needs lysine to build proteins, but can’t manufacture it. (We absorb small amounts from red meat and milk.)
The University of Maryland says doses of up to 3,000 milligrams three times daily are the norm for shortening a painful outbreak; 1,000 milligrams per day may prevent recurrences. About 90 percent of adults carry the HSV-1 virus that causes nasty cold sores to flare up at the worst times: on vacation, before weddings, and during an illness. Research suggests that lysine keeps the virus from spreading. Prescription antivirals (Zovirax, Denavir, Famvir, and Valtrex) are FDA-approved for fighting HSV-1. Both lysine and prescription products are most effective when taken at the first sign of a cold sore.