- L-Lysine works by competing with the absorption of arginine. Arginine is necessary for the herpes to reproduce, but a cat can easily use the lysine instead of arginine. So, if the system is flooded with lysine, the herpes can't reproduce.
- A newer theory is the cat's cells need lysine to use the arginine in the cell. By giving the cat extra lysine, the cat is assured of having enough lysine to use up all the arginine in the cells, thus depriving the herpes of the arginine. No arginine, no little baby herpes viruses.
The lysine itself is available in 3 forms:
- treats -- The treats are laced with lysine and many cats do like them. The average cat needs at least 6 treats per day for maintenance (at least in one brand) and they are not cheap.
- gel -- Similar to hairball remedy, lysine is available in a tube. The gel, which has only a slight taste (yes, I tried it), is not objectionable to most cats. None of mine will eat it off my finger, but if mixed in food or put in a syringe, they will eat it. It is moderately expensive and because it is mixed in a wet medium, it does expire.
- powder -- The powder itself comes in 3 forms. Capsules of pure lysine from a health store. The capsule is opened and spread on wet food. Bulk lysine (for people) in a jar from a health store or online. Usually 1/4tsp is 500mg. And lysine powder for pets. The lysine for pets is the cheapest and may work for most cats, except, of course, one of mine. The lysine is listed as "in a palatable flavor base" and that's it. This is one of my problems with 'pet' supplements -- the labelling is much less strict. The "base" turned out to be whey powder, which Clancy cannot tolerate. I put one dose on some food and within 30 minutes his face was swollen, he was drooling, and he was lethargic. He did survive and he can tolerate lysine -- pure lysine -- so it was the whey powder which caused the problem.
In general, cats do tolerate the lysine well. I have heard some people say their cats do not tolerate it and get either diarrhea or vomiting. I am curious to find out what form they tried and if that was not the problem as opposed to the lysine itself.