Propranolol is part of a class of drugs called beta-adrenergic blocking agents, or beta blockers for short. As the name implies, beta blockers block beta receptors in the body. Beta receptors are located in a number of places within the body, including the heart and blood vessels. These receptors are what stress hormones (such as adrenaline) attach to and cause certain reactions in the body, such as an increase in:
- Heart rate
- The force with which the heart pumps blood
- Blood pressure (both systolic blood pressure and diastolic blood pressure).
By blocking beta receptors, propranolol causes the reverse effect of stress hormones. It decreases heart rate and both systolic and diastolic blood pressures, as well as the heart's workload. This means that the heart requires less blood and oxygen to work properly.
For people with migraines or an essential tremor, it is not known exactly how propranolol works. However, beta receptors in the brain may be involved.
By lowering blood pressure, propranolol can decrease the risks that accompany long-term high blood pressure (see Effects of High Blood Pressure). By decreasing the heart's workload, the medication can also decrease symptoms of angina, including chest pain. Although the exact mechanism is not known, propranolol can increase the survival rate in people who have just suffered a heart attack.