Beta-blockers are so called because they block adrenaline beta-type receptors in certain cells around the body. These beta-receptors respond to adrenaline produced by the adrenal glands and nervous system in response to anxiety, shock and fear.
Beta-blockers are commonly used in heart patients but are also used by people who have palpitations through anxiety or metabolic diseases such as hyperthyroidism. In themselves they are not particularly dangerous drugs unless taken in overdose or taken by asthmatics. It is contraindicated to use these drugs if you have any suggestion of asthma.
Once again, these drugs deal with the symptoms and not the underlying cause and alternative treatments are available but withdrawal should be done only under medical supervision.