@SarahGen-- If you get cold sores back to back, I think you can take lysine as a cold sore medication for a longer period of time. Just don't take more than the daily recommended dose. I'm not a doctor though, so you should ask your doctor for proper advice. I take 1000mg/day when I get a cold sore and I keep taking it until it's completely gone. I also take a multivitamin with vitamin C on a regular basis to keep my immune system strong. The immune system has a lot to do with cold sores.