Honestly, I think it’s between you and your doctor to decide if your anxiety is enough that you need medication to assist you in developing more effective techniques to cope with it during shows. (And for folks who just ‘take a swig’ - alcohol used in such a fashion is essentially medicating the anxiety, also. It’s just that drinking tends to be more socially acceptable than taking a pill, even though the dosage of the pill can be much more carefully regulated. How much actual alcohol is in a ‘swig’ depends tremendously on what your idea of swig is, and what your drink of choice is.
)
That said, I suspect that unless you do have a proper generalized anxiety condition which is causing problems in multiple areas of your life which calls for a different sort of medication, the best approach to the problem would be to couple the anti-anxiety medication with some form of therapy with the goal being to get you to a point where the medication was no longer necessary.
So I would be uncomfortable with a doctor who just wrote a script and sent you on your way. This IS supposed to be something we do for fun/enjoyment, and while occasional bumps can turn up in the road from negative experiences or anxiety in other areas of life spilling over, if you have to drug yourself to the gills each and every time to get through it, maybe you’re not doing the right thing. (I mean, if someone had a horse that was a total basket case every time it went to a show, people would suggest different things to get him used to it, but at some point you just have to say ‘this isn’t his thing.’ Same with people. Nothing wrong with deciding that something just isn’t what YOU want to do with horses, even if it was what you wanted to do at a different point in time. People change, situations change, etc.)
All of that said - if you are doing ANYTHING that is supposed to help with your nerves (alcohol, supplements, medications) I would never ever dream of trying it for the first time in a show environment. Test it out at home first - preferably not actually on or around a horse to start with. You should know how what you’re taking is going to influence you LONG before you take it in a show environment where you’re endangering yourself, your horse, and anyone else around if something goes wrong.
(And take it with someone else observing you - YOU might feel fine, but not be, if the medication is messing with your perception. How many drunk drivers swear they’re perfectly okay to drive when they clearly aren’t?)