Before any of the polygraphs I have taken, the examiner always asked if I was taking any medications, what were they for, when was the last time I had taken any, etc.  He also asked when was the last time I had consumed any alcoholic beverage.   

As for the question about anti-anxiety drugs, and whether they would help, I don't know.   Personally, I wouldn't take any drug unless a Doctor prescribed it, and I absolutely wouldn't lie about it.   

Good luck.

Kona

Keep in mind that with many medications, relaxed = sedated (I don't know anything about the herb mentioned).

I wouldn't consider being sedated as a benefit.  I would expect you'd likely have inconclusive results because of it.   

Anyway, I think most examiners will ask you if you'd had any medication in the last 24 hours.  I'd say if you told him/her you'd taken anti-anxiety medication they might disqualify you (consider it an attempt to cheat) or at the least schedule you for the test at a later date.  I'd stay away from it.  If you're going to attempt countermeasures just read about cognitive countermeasures as you're least likely to get caught attempting them.