Very, very, very bad idea! You absolutely should never use beta blockers unless a physician has prescribed them to you, and I'm not talking about hounding your doctor for beta blockers—if there is a legitimate medical reason (eg high blood pressure) for you to be taking these drugs, your physician will recommend them to you. Otherwise, don't touch the stuff.
n4mwd: Beta blockers lower blood pressure and inhibit epinephrine. As such, many people use beta blockers (legally and otherwise) as performance enhancers to reduce stress, especially in audition situations. This is not an appropriate use of the drugs, and can be very dangerous. I know an aspiring musician (small little guy with already low blood pressure) who takes a half-dose of beta blockers before auditions. After the audition is over, he basically goes unconscious the rest of the day. Others have messed themselves up much worse.
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WAR IS PEACE
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IGNORANCE IS STRENGTH