I use this for cats with feline herpes to help keep outbreaks at bay, so having a subscription option is awesome. This comes in powdered form, which is what you need to sprinkle into their food. The price is also comparable to what I find in store. And while it helps with feline herpes, I also dip into their stash when I feel a cold sore coming on. I've used lysine for years to help fight cold sores and the stuff works like a hot damn.
UPDATE: Recent research suggests that there may be a link between high doses of lysine and kidney problems, so I think I'll be saving the Lysine for outbreaks instead of maintenance for my cats.