I use this with Skye as she is sometimes so nervous she overgrooms. It took a while to kick in but does seem to help her a lot.
Once I had to stop her dose for a little while but then put her back on again, the second time round I could see the difference within 48 hours.
When I transported the cats on a 3 hour train ride they had been on zylkene for about 10 days before hand, they all travelled really well, even Yogi, who usually yells his head off when he is in his carrier.
I did have Skye checked at the vets before I started her on Zylkene and discussed it with him.