I agree with the above reply, with the exception of the info that propanolol needs to be taken daily. Beta blockers like Inderal are often prescribed "as needed" to combat stage fright, presentation anxiety. They're usually prescribed to be taken within a certain time frame (usually an hour or so) before the anxiety causing event.
I do agree that taking both medications isn't necessary, and could exacerbate symptoms of drowsiness, dizziness, etc. One or the other should be effective. If they're both prescribed, then just try one medication one time, to see how it works, and the other on a subsequent occasion.
Let us know what you decided and how you're doing! Good luck!
First off I wanna ask did your doctor specifically prescribe the propranolol to be taken on an as needed basis or are you taking it daily? Typically this class of medication is to be taken daily due to its effects and the potential for complications from taking it irregularly. I do not recommend taking these two medications together at the same time because they both lower blood pressure and could cause you to feel faint, dizzy, or lightheaded especially with this being a new combination. If you are not taking the propranolol daily you could always try the xanax alone prior to the presentation and see how it affects you, but if you are taking the propranolol daily I think it would be best to space the medication and take them separately. As with any meds you could always contact your physicians office and speak with the nurse and determine what would be the best option for you. Good luck on your presentation and try to remain as a calm as possible!