herbal & aroma therapy??

What do y'all think of the use of herbs and essiental oils as medications and calming agents in horses?

I'm not an expert in this, but I believe they can be very helpful.
Of course, they are by no means, magical potions that can cure horse behavioral problems.
But they can definitely be very calming and pleasant to the horse.
I've started researching herbs that are good for my horse, he loves the smell of most of the herbal oils. I am interested in what other people on this forum have to say, as well.

A local store has started selling the Annie Oakley muzzle oils. I just wondered what more experienced riders and horsemen/women thought.

I'm using herb mix (just a little) as a calmer. I tried lavander oil while back before trailering (someone swear it helps if you put couple drops on horse's head), but it didn't do a dime for me.

This store sales the lavender oil. I bought a small bottle ($5), but haven't used any yet. I've seen some ads in "Horse and Rider" for a herbal calmer, but didn't know if they actually worked.