Honestly, I would stay away from any sort of medication. Train your body like any other "athlete" would do (the natural and healthier way) and you'll be fine 🙂
Being anxious and having a flood of information filtrating your brain at every minute winding up to the day of the exam is unavoidable, so the best thing to do is know that it is going to happen, and don't let it overwhelm you. The best thing I suggest for this is don't allow yourself to be alone with your thoughts the whole day! Ok this sounds funny, but it's true. Have just enough alone time to stay focused, but make sure to make phone calls, or just hang out with your good friends that will help you keep you relaxed, while their still understanding that you can't just kill the stress with a couple of beers 😉
As for me, the day of the test I did some light reviewing, I did about an hour of swimming to release some stress, came home and got ready to take off; (since my testing center was about an hour from my house, I decided to stay at a nearby hotel with my best friend). IT'S THE BEST DECISION I COULD HAVE MADE!! Not only did I not have to worry about traffic or possibly oversleeping (I was only 5 mins away) but staying with my best friend kept me relaxed...I didn't have time to overthink or psych myself out since I was too busy chatting away with her and cracking jokes, all the while she comforted me and boosted my confidence about my abilities...I had a bit of trouble falling alseep (as I predicted) but it was nothing like I had experienced on prior night-before-the-test nights. Plus, since I wasn't in the comforts of my own home, i wasn't tempted to stay up and watch my usual TV programming, so I ACTUALLY got to bed at 10:30 (compared to my usual bedtime of 2am!)
Another thing that can help is to mentally prepare the week of the exam for the possible thoughts and anxieties you might have the night before...doing this I actually had the "I woke up late/i blanked out/did horrible" nightmare about two days prior to the test...I was happy to have gotten it out of the way! lol
For anthing in life, knowing what to expect (or running through the possibilities ahead of time) is always more comforting, thus avoiding any major surprises. This is why everyone says to do practice tests, and try to take them as serious as you would the day of the exam. So a couple weeks prior, focus on practicing all other factors revolving the test: sleeping times, thought processes, meals, even maybe getting used to watching a specific show every night or talking with the same person that you know will instill positive and relaxing thoughts...
Hope all this helped (I know, it's long...sorry) and best of luck!!!