Best calming drug to use for shows?

I'm doing just a small, local hunter show in a few weeks, but my horse is not slow by any means. We're doing an 2'6 division but she jumps like a jumper at shows.. speedy! I would show her in jumpers but I lease her and her owner only wants her to be a hunter (which she's clearly not). Sucks, but I just gotta deal with it. ANYWAYS, at home she usually gets excited when it comes to jumping, but allows you to control her much better. At shows on the other hand, it's like someone lit a firecracker inside of her. I was wondering what are some good calming supplements/drugs? I'd prefer it be a paste, like the Calm N Cool one (which I have heard works, but someone said it's only for about an hour?). Thanks!!