Epinephrine vs. Norepinephrine: What's the Difference?

Epinephrine and norepinephrine are chemicals naturally made in the body that help turn on our fight-or-flight response to stress. They function as both hormones and neurotransmitters. Having too little or too much of either can have different effects on your health.

Both epinephrine and norepinephrine are also available as medications to use in emergency situations, such as with certain types of shock or at times of critically low blood pressure. They both work on the alpha and beta receptors. However, they have slightly different functions and uses in the body.

This article will discuss the similarities and differences between norepinephrine and epinephrine, including their functions, medical uses, and effects on overall health.

Norepinephrine vs. Epinephrine: How Do They Function?

As hormones, norepinephrine and epinephrine travel through the bloodstream to reach and turn on signals responsible for regulating the fight-or-flight response (physiological changes by the body in response to stress or fear).

As neurotransmitters, they are chemical messengers sending signals between nerve cells to activate the autonomic nervous system. The autonomic nervous system is responsible for controlling certain systems in the body, such as heart rate, breathing, and digestion. 

Epinephrine

While both norepinephrine and epinephrine can activate alpha and beta receptors, epinephrine has a stronger effect on beta receptors. The beta receptors are located in the heart, lungs, and skeletal muscle.

Epinephrine helps the body respond to stressful situations by altering the function of vital organs to keep us alive. When the brain feels a sense of danger, the autonomic nervous system tells the adrenal gland to release epinephrine into the bloodstream. When epinephrine is released, the body feels the adrenaline rush that causes increased heart rate, fast breathing, elevated blood sugar levels, and increased physical strength.  

Norepinephrine

In contrast, norepinephrine has a more dominant effect on alpha receptors primarily located only in the arteries. While norepinephrine is always present in our blood in small amounts, during stressful situations, the adrenal medulla releases more of it.

The constant, steady release of norepinephrine helps maintain blood pressure. However, during times of stress, the adrenal medulla releases more, which raises blood pressure further.

Norepinephrine stimulates the alpha receptors in the arteries. When alpha receptors are activated, the arteries constrict, or squeeze, the blood vessels, leading to an increase in blood pressure.

What Are the Medical Uses of Norepinephrine and Epinephrine?

Even though norepinephrine and epinephrine are naturally made in the body, these two chemicals can act as medications when needed in emergency situations.

Levophed (norepinephrine) is a first-line treatment that can raise blood pressure when experiencing severely low blood pressure or shock. This is because of its dominant effect on activating the alpha receptors in the arteries, which helps restore blood flow and blood pressure.

Common uses of Levophed include:

• Cardiogenic shock: When the heart is unable to pump blood throughout the body
• Septic shock: When the blood pressure drops to extremely low levels due to an infection
• After a cardiac arrest: When your heart stops beating
• Hepatorenal syndrome: A liver disease that can lead to kidney failure, with a combination of these conditions causing a drop in blood pressure

Adrenalin (epinephrine) is used to help restore oxygen and blood flow by increasing blood pressure and opening up your airway.

Compared with norepinephrine, epinephrine has a greater effect on activating beta receptors at low doses. Activation of beta receptors can open up airways, increase heart rate, and widen blood vessels.

Epinephrine is a lifesaving medication used in the following critical situations:

• Anaphylactic shock after an allergic reaction (people who are at high risk of anaphylaxis commonly carry an EpiPen, in case a severe reaction would occur) 
• During a cardiac arrest
• Severe asthma attack
• Critically low blood pressure or shock 

What Happens With Too Little Norepinephrine or Epinephrine In Your Body?

Certain factors can lower your norepinephrine and epinephrine levels. Low levels of norepinephrine or epinephrine can affect your physical and mental state.

Low Norepinephrine Levels

Low levels of norepinephrine can cause:

• Lack of energy
• Concentration problems
• Depression

A rare genetic disease that prevents the production of norepinephrine is called dopamine beta-hydroxylase deficiency. This disease causes low levels of norepinephrine by preventing the conversion of dopamine to norepinephrine.

Common symptoms of this disease include: 

• Drop in blood pressure when standing up (orthostatic hypotension)
• Fainting
• Drooping of both upper eyelids (ptosis)
• Difficulty maintaining body temperature
• Nasal congestion
• Difficulty sleeping 
• Low blood sugar

Norepinephrine in the brain can help aid in focus and organization. Therefore, the lack of norepinephrine can result in the development of attention deficit hyperactivity disorder (ADHD).

Low Epinephrine Levels

Having too little epinephrine in the body is rare. 

One disease that can lower the levels of epinephrine is Addison’s disease. Addison’s disease suppresses the adrenal gland, which normally produces hormones such as cortisol, aldosterone, and epinephrine. Common side effects of Addison’s disease include: 

• Darkening of the skin due to cortisol loss
• Shaking or tremors
• Depression
• Decreased appetite
• Low blood pressure, especially when standing
  

What Happens With Too Much Norepinephrine and Epinephrine?

While epinephrine and norepinephrine can help you in intense situations, too much can put your mind and body on edge.

Certain factors may increase levels of norepinephrine and epinephrine, such as:

• Tumors on the adrenal glands
• Obesity
• Chronic stress

High Norepinephrine Levels

Symptoms of high levels of norepinephrine can include:

• Euphoria
• Anxiety
• High blood pressure
• Hyperactivity

High Epinephrine Levels

Symptoms of high levels of epinephrine include:

• High blood pressure
• Rapid heart rate
• Anxiety 
• Weight loss
• Tremors or jitteriness

Summary

Epinephrine and norepinephrine are naturally made hormones and neurotransmitters that regulate the autonomic nervous system. Both can also be used as medications for life-threatening situations such as shock or critically low blood pressure. 

The main difference between norepinephrine and epinephrine is the receptors they activate.

Norepinephrine and epinephrine can activate both alpha and beta receptors. However, norepinephrine is better at activating the alpha receptors in the arteries, making it ideal for increasing blood pressure. Epinephrine, on the other hand, has a greater effect on the beta receptors, which are located in the heart, lungs, and skeletal muscle.

Although they are slightly different, both chemicals play essential roles in the body and are used for similar purposes.

The author would like to recognize and thank Alexya Rosas for contributing to this article.