Does Passion Flower really calm a horse down?

I was reading this in a magazine article... what have you heard about this? If you have used it, how much did you give your horse, and where did you buy it?

I am looking into it because my horse gets a bit stressed at the shows... Maybe this will help?

Thanks!

To be honest, I don't think so. I'm using calm agent on my horse, and I notice chammomile + vervain seem to be the best. Everything else is not very useful (and mix with garlic drove her crazy 2 times I tried it). AND you have to give those herbs for at least a week to see the effect. So for just a show your best bet would be those one-time tubes with paste (Quietex or whatever the name of it). BTW, don't rely much on those either - calming is a very individual thing and what works for one horse has no effect on another.