Epinephrine and norepinephrine belong to a group of compounds known as catecholamines. These compounds act as both neurotransmitters, delivering signals between nerve cells, and hormones.
Epinephrine and norepinephrine have similar chemical structures. However, they produce different effects on the body. Both play a role in the regulation of the sympathetic nervous system, which is responsible for the body’s “fight or flight” response.
Another name for epinephrine is adrenaline, and some refer to norepinephrine as noradrenaline.
In this article, we discuss the similarities and differences between epinephrine and norepinephrine, along with their functions and medical uses. We also outline the health effects of having too much or too little of either compound in the body.
Both epinephrine and norepinephrine are chemical messengers. They function as hormones, as well as neurotransmitters.
As hormones, epinephrine and norepinephrine travel through the bloodstream, along with other hormones that the endocrine and reproductive organs make. They tell organs and tissues to work in different ways.
Neurotransmitters have a similar function. However, they only occur in nerve cells and travel across synapses, which are junctions where two nerve fibers meet. Nerves cells produce neurotransmitters in response to electrical impulses.
The adrenal medulla is the inner portion of the adrenal gland. It regulates and secretes both epinephrine and norepinephrine in response to stress and other imbalances in the body, such as low blood pressure.
What does epinephrine do?
When the brain perceives danger, the amygdala triggers the hypothalamus to activate the autonomic nervous system (ANS).
Signals from the ANS stimulate the adrenal gland to start pumping epinephrine into the bloodstream. People often refer to this surge of epinephrine as an adrenaline rush or the fight or flight response.
Epinephrine activates alpha- and beta-adrenoreceptors in the cells of various body organs and tissues, including:
- the heart
- the lungs
- the muscles
- the blood vessels
The release of epinephrine into the bloodstream brings about several physiological changes, such as:
- increased heart rate and blood flow
- faster breathing
- raised blood sugar levels
- increased strength and physical performance
What does norepinephrine do?
The adrenal medulla produces norepinephrine in response to low blood pressure. Norepinephrine promotes vasoconstriction, which is a narrowing of the blood vessels. This, in turn, increases blood pressure.
Like epinephrine, norepinephrine also stimulates alpha-adrenoreceptors in the cells of the blood vessels. It increases heart rate and blood sugar levels.
Synthetic forms of epinephrine and norepinephrine have several medical uses.
Doctors prescribe epinephrine to treat severe medical conditions that affect the heart and airways, such as anaphylaxis.
Anaphylaxis is a severe and life threatening allergic reaction that can interfere with a person’s ability to breathe. Epinephrine counters anaphylactic shock by:
- narrowing the blood vessels to increase blood pressure
- increasing heart rate to improve blood flow
- relaxing the muscles and airways, allowing a person to breathe
People at risk of anaphylaxis can carry an epinephrine autoinjector with them at all times.
Doctors may also use epinephrine to treat the following:
During asthma attacks, doctors use epinephrine in a nebulized or inhaled form, rather than injecting it.
In cases of septic shock, doctors may use epinephrine and norepinephrine at the same time, delivering it via an IV line.
Norepinephrine can help raise systolic blood pressure (SBP) in people who have had a heart attack. Systolic blood pressure refers to the pressure that occurs when the heart is contracting and ejecting blood. A heart attack can damage and weaken the heart muscle, resulting in low SBP.
Doctors may also use norepinephrine to treat the following:
- Critical hypotension: This is the medical term for dangerously low blood pressure.
- Septic shock: This is a life threatening condition in which blood pressure drops dangerously low following an infection. Doctors may combine norepinephrine with IV fluids and antibiotics to treat septic shock.
- Pericardial tamponade: This is another life threatening condition in which the heart is unable to fully expand and fill with blood due to fluid in the pericardium, which is the membrane surrounding the heart. Doctors treat it via pericardiocentesis, which removes the excess fluid, as well as norepinephrine.
- Neurogenic shock: This occurs when damage to the nervous system causes difficulty maintaining a stable heart rate, blood pressure, and temperature.
Certain factors can affect the body’s ability to produce or respond to epinephrine and norepinephrine, including:
Additionally, a rare condition known as genetic dopamine beta-hydroxylase deficiency (GDBhD) prevents the body from converting dopamine into norepinephrine.
According to a 2018 review article, GDBhD results from a mutation in the norepinephrine transporter gene g237c. The authors concluded that this condition might decrease sympathetic nerve activity and increase the risk of damage to the heart and blood vessels.
Low levels of epinephrine and norepinephrine can result in physical and mental symptoms, such as:
- changes in blood pressure
- changes in heart rate
- low blood sugar, or hypoglycemia
- migraine headaches
- problems sleeping
In addition, norepinephrine plays a role in focus and promotes periods of sustained attention. Low levels of norepinephrine may contribute to the development of attention deficit hyperactivity disorder (ADHD).
The following medications can increase levels of norepinephrine:
- amphetamines, such as methylphenidate (Ritalin) and dextroamphetamine (Adderall)
- serotonin-norepinephrine reuptake inhibitors (SNRIs), such as venlafaxine (Effexor) and duloxetine (Cymbalta)
Certain medical conditions can affect the adrenal glands, causing excess production of epinephrine and norepinephrine. Examples include:
Symptoms of high levels of epinephrine or norepinephrine can include:
- excessive sweating
- rapid or irregular heartbeat
- high blood pressure
- jitteriness or shakiness
- intense headaches
- pale or cold skin
A 2018 review article states that having high levels of norepinephrine can increase a person’s risk of cardiovascular and kidney damage.
An epinephrine overdose can occur in people who use epinephrine injections to treat certain medical conditions. An overdose of injected epinephrine can lead to dangerously high blood pressure, stroke, or even death.
Epinephrine and norepinephrine are similar chemicals that act as both neurotransmitters and hormones in the body. Both substances play an important role in the body’s fight or flight response, and their release into the bloodstream causes increases in blood pressure, heart rate, and blood sugar levels.
Epinephrine acts on the alpha- and beta-adrenoreceptors in the muscles, lungs, heart, and blood vessels. Norepinephrine is a metabolite of dopamine that primarily acts on the alpha-adrenoreceptors in the blood vessels.
Doctors may prescribe epinephrine to treat potentially life threatening conditions, such as anaphylaxis, severe asthma attacks, and cardiac arrest. A doctor may prescribe norepinephrine to raise dangerously low blood pressure following a heart attack, critical hypotension, or septic shock.