The general definition for sympathomimetics is a substance that imitates the activated sympathetic nervous system. The sympathetic nervous system is a part of the autonomic nervous system, or the nervous system that is not under conscious control. This part of the autonomic nervous system is activated in response to danger and prepares the body to react to the dangerous situation. This is also known as the “fight or flight” response.
Basically, the sympathetic response temporarily shuts down processes that might slow a person down, such as food digestion or urine production. This response also speeds up processes that allow for bursts of energy, such as increased heart rate, increased blood pressure, increased blood to the brain, and rapid glycogen hydrolysis for muscle energy. In addition, the bronchial tubes will become dilated, or widened, in preparation for a greater oxygen requirement.
The term sympathomimetics usually refers to substances used as sympathomimetic drugs. Medical use of sympathomimetics is usually limited to serious or life-threatening conditions, such as treatment for a heart attack, dangerously low blood pressure, hemorrhagic shock, or a severe asthma attack resulting in the inability to breathe. They may also be used to prevent the onset of premature labor.
Catecholamines are the most common group of sympathomimetics, and include epinephrine, norepinephrine, and dopamine. Epinephrine, or adrenaline, is a hormone produced naturally by the body in response to fear or strong anger and is a frequently used sympathomimetic drug under the emergency conditions described above. A natural intermediate in the body during epinephrine synthesis is dopamine, a catecholamine best known for its effects on the brain. Dopamine can be used medically to help relieve some of the symptoms of Parkinson’s disease.
Sympathomimetics can also be used as appetite suppressants for the treatment of people who are morbidly obese. Because the appetite-suppressing effects of sympathomimetics usually last for just a few weeks, they are only effective as a short-term solution. Other examples of sympathomimetics are illegal stimulant drugs like cocaine and methamphetamine.
The long-term use of sympathomimetics can be very dangerous. In addition to their generally addictive nature, their strong stimulatory effects on the nervous system can result in high blood pressure, a dangerously high heart rate, and an abnormal heart rhythm, or cardiac arrhythmia. For these reasons, these types of drugs are only used in the short term and usually only under emergency conditions. In addition, they should be used only under constant medical supervision.