Congratulations Monica! You are now at the start line of this marathon run!
I thought I'd share some relevant thoughts, without getting into pharmacology, on the topic of beta-blockers since a few musicians are already curious...
Never take beta-blockers without consulting a physician. If you're intent on using them, you have to experiment with the dosage in different situations under medical supervision, way before any performance. These medications, such as propanolol (inderal), block the adrenaline (epinephrine) receptors that cause the "fight-or-flight" response. Blocking beta receptors can cause lower heart rate, decreased force of heart contractions, bronchial constriction, uterine contractions, decrease blood pressure, decrease in tremor, and relieve migraines. If a patient has asthma, diabetes, Raynaud's Phenomena, or congestive heart failure, beta-blockers should NOT be prescribed.
The side effects are minimal when used in lower doses, but may include dry mouth, low heart rate and blood pressure, rash, cold extremities, fainting, lethargy, etc. Beta-blockers don't inhibit cognitive abilities. They don't improve your muscle timing. A musician's response may vary due to dose and/or efficacy. Peak response occurs in 1-1.5hrs, so you need to time it just right.
I've never took them or needed them myself. However, there are other options if you don't want to take medications. A Non-Medication Approach:
Redirect your anxiety in convincing yourself that you have a story to tell. Use your talent, technique, and understanding of the music to conquer the judges and audience. Identify your anxiety symptoms - sweaty palms, racing heart, shallow/rapid breathing, forgetfulness, upset stomach, etc.? For example, if you have rapid breathing or heart rate, learning relaxation techniques prior to a performance will help. Or if you have nausea or other stomach problems, taking a simple pill to calm your GI might help. Positive thoughts and reminding yourself of your strengths can reduce negative thoughts as well.