This is a great site for that kind of information...
It defaults to a search by med name, but choose the Conditions tab to see all meds/supplements rated for a specific condition. The thing that I absolutely love is the reader comments. Pretty enlightening.
I found out accidentally that Vitamin B6 can stop/decrease an mild anxiety attack (the kind where you suddenly feel a swell of anxiety and your heart starts beating fast). Don't know if that was just how it affected me, or whether anyone else would get that kind of result. It tastes pretty horrible, but when I put a 1/4 tablet under my tongue and covered my eyes (or even better, went in a dark room), it would go away in less than 10 minutes. Swallowing it works too but much slower.
I'm not sure that I've had a real Panic attack. I've been trying to figure out how that is different from an anxiety attack. Is a panic attack when you suddenly feel like you are dying?