My sister used to get them a lot when she was a kid (in the 70's). My mom would give her L-lysine and have her rinse her mouth with glysine. She would get them from eating too much citrus. Now she gets them when she's stressed. L-lysine is an amino acid and doesn't produce any side effects that I'm aware of. I was able to take 3,000mg per day while I was pregnant. I take it when I feel a coldsore coming on along with extra B12 and it stops it in its tracks. L-lysine is great for herpetic lesions and shingles. You can mega dose it by taking 1,000 mg 3-4 times a day.