Different parts of the body contain different beta receptor subtypes, designated beta1 and beta2. Receptors in the circulatory system belong to the beta1 subclass, while those on cells lining the small airways of the lung are of the beta2 subclass. Beta2 receptors help relax these small airways and therefore make breathing easier-indeed, patients with asthma and other obstructive lung diseases often inhale beta2—stimulating medications to help them breath more easily. Thus, patients with such diseases should not take medications that block beta2 receptors. Fortunately, several blood pressure medications that selectively block only beta1 receptors are now available.
Beta-blockers are also probably not the best choice of treatment for people who have diabetes along with their high blood pressure or angina. In a hypoglycemic crisis (where blood sugar drops too low), the body pours out large amounts of epinephrine to stimulate release of stored sugar into the blood stream. This epinephrine also causes a rapid, pounding heartbeat that is often the diabetic's first indication something is wrong. Beta-blockers blunt both responses, leading to a crisis that is worse and longer-lasting than it would be otherwise.
These medications may likewise not be the best choice for people with poor circulation in their hands or feet, since beta-blockers sometimes make circulation in the extremities even worse.
About 10% of patients treated with beta-blockers may become dizzy or light-headed. More seriously, about 5% may become clinically depressed, with feelings of helplessness and hopelessness that sometimes lead to suicide. As might be expected, all such reactions are less common with beta-blockers that do not enter the brain readily.
Other moderately common side effects of beta-blockers include diarrhea, rash, slow heartbeat, and impotence or loss of sexual drive.
An additional concern with beta-blockers is their effect on blood cholesterol, they lower the amount of "good" (HDL) cholesterol, while increasing the amount of "bad" (LDL) cholesterol. They also raise the amounts of fatty materials known as triglycerides in the bloodstream; some scientists believe triglycerides may increase the risk of a heart attack to almost the same extent as cholesterol. Nevertheless, there is no concrete evidence that people treated with beta-blockers are more likely to have heart attacks than those treated with other blood-pressure medications.
Recent studies indicate that beta-blockers are actually underused. While clinical evidence shows that beta-blockers are in fact very effective medications, other blood pressure drugs are prescribed more often. One reason they are under prescribed may be that physicians are wary of potential side effects when patients are given recommended doses. A new study, however, has provided preliminary evidence that beta-blocker medications can still provide positive clinical outcomes at lower doses, making the risk of side effects lower. Some beta-blocker medications are, however, commonly used. Inderal (Propranolol), Lopressor (Metoprolol), and Ternormin (Atenolol) are widely used beta-adrenergic blocking agents. In general, the generic names for this class of drugs end with the suffix -olol, as in Propranolol.