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In order for an erection to occur, there has to be activation of beta-receptors in the tissues of the penis and arteries of the penis. Some beta blockers bind to many different type of beta-receptors and can often block those receptors(beta-2). That does not allow the blood vessels to relax enough to allow the penis fill up with blood for a proper erection. Propanolol, timolol, and nadolol are non-selective beta blockers and have the most potential for interfering with an erection. Beta blockers that are called 'cardio-selective' are those that only block the beta-1 receptors and do not tend to cause ED. Examples of cardio-selective beta blockers are metoprolol, acebutalol, esmolol, and atenolol. Some beta blockers also block certain alpha receptors as well, which can cause ED. Examples of these are carvedilol and labetalol. But there are some beta blockers that can actually help erectile function by increasing nitric oxide (NO) levels with their alpha-blocking properties, such as nebivolol. Interestingly, studies have shown that just having anxiety about having side effects is enough to produce the side effect. Studies also have demonstrated a placebo (sugar pill) worked just as well as Viagra to get rid of the ED associated with beta blockers.