I have found Comfort Zone to be amazing. Libby was never afraid of thunderstorms until she turned 3 years old. No reason that I can come up with...she just suddenly became terrified of them and other things like fireworks. I got her a thundershirt which seemed to help a little, but she was still very scared. I bought a bottle of spray Comfort Zone and if I spray a little of that in the room when there is a storm, she goes from being anxious and scared, to sleeping! This comes in either a spray or a diffuser which you plug into an outlet and I guess it just lets a little out every now and then. Here's a link to it on Amazon...for the diffuser...and if you look down that page, you will see the spray also.
Comfort Zone with D.A.P. Diffuser for Dogs, 48... I did use this when she also was wearing her thundershirt. Next storm I'm going to try it without the thundershirt and see if that works.