So far I have not been able to find any studies about the efficacy over time of the feliway diffuser on google (of course, typing in "synthetic fraction of F3 fraction of feline facial pheromone" in my search). At least unlike revolution, which costs $30/month for my three kitties (3.3 cents per day per cat, and to treat three cats approximately 10 cents per day), feliway is a product that does not cost more when you have more cats . In fact, at $18.79 with a four week duration of use, the feliway refill costs only 6.7 cents per day for one cat, and for three cats, that works out to 2.23 cents per day per cat. So like so many things, it's only pennies per day!!! There, that will have everyone feeling much better no doubt. Also if you do the math, you can justify the cost of many purchases using the pennies per day theory, even a new Ferrari (assuming you drive it for a long long time)!!! I should know, I can rationalize the purchase of almost anything!!!