The Chemical Imbalance Theory

Depression is a complex disorder that cannot be simplified to a chemical imbalance in the brain.

Depression is a major mental health issue that affects approximately 14.8 million adults in the United States. In an effort to develop better treatment options for this disorder, scientists and clinicians have worked for many years to determine the cause of depression.

During this work, there was a theory that depression is associated with variations in the level of neurotransmitter chemicals in the brain. This variation is known as a chemical imbalance, but what is a chemical imbalance, exactly? Simply put, a chemical imbalance occurs when there are too many or too few neurotransmitters in the brain.

Symptoms of a Chemical Imbalance

Neurotransmitters are chemicals that are released from nerve cell endings and travel to surrounding nerve cells to relay a signal. The signal travels to different areas of the brain, which creates emotions or causes a physical response. 

Neurotransmitters have many different functions and can act on many areas of the body. Chemical imbalance symptoms include:

• Feeling sadness or hopelessness
• Lacking energy
• Having the inability to concentrate 
• Being agitated or irritable
• Changes in appetite
• Changes in sleep patterns
• Having feelings of imminent danger
• Feeling numb or lacking compassion
• Severe mood swings
• Thoughts of suicide or hurting others
• Inability to carry out day-to-day tasks
• Getting emotional or crying uncontrollably for no reason
• Withdrawing from regular activities and social activities
• Drastic changes in behavior
• Lacking interest in things that you usually enjoy doing
• Feeling anxious or nervous 

Feelings of depression or anxiety can lead to suicidal thinking. If you or a loved one is experiencing suicidal thoughts or tendencies, call the National Suicide Prevention Hotline at 1-800-273-8255.

The Role of Brain Chemistry in Depression

There are certain parts of the brain that control mood and emotions. These parts of the brain, which include the hippocampus, thalamus and amygdala, are believed to be affected in people with depression. The parts are responsible for long-term memory, sensory information and emotions such as anger, pleasure, sorrow and fear.

Variations in neurotransmitter levels are what cause a chemical imbalance in the brain. Altered levels of neurotransmitters can affect the intensity of signals between nerves. A weakened signal can occur when a nerve ending doesn’t make or release enough of a neurotransmitter. Once the neurotransmitter is released, it can be reabsorbed too quickly by the nerve endings, which would also weaken the signal. The responding cell could also have altered receptor levels, causing increased or decreased reception.

Scientists believed chemical imbalance and depression were linked, due to how imbalances affected regions of the brain that control mood. The chemical imbalance theory is that depression correlates with low levels of neurotransmitters called serotonin and norepinephrine.

The Reality Behind the Chemical Imbalance Myth

The chemical imbalance theory developed when drugs that targeted neurotransmitters were able to relieve depression symptoms. For example, monoamine oxidase inhibitors (MAOIs) increase the number of neurotransmitters and can treat depression in some patients.

However, recent scientific evidence has failed to prove this theory. The only evidence is that people with depression have fewer neurotransmitters in their blood, and depression symptoms are relieved in some patients through medications that increase neurotransmitters. 

These findings are not always consistent and may not explain the underlying biology of depression. First of all, medications that increase neurotransmitters are not effective for all patients. This suggests that there are other factors contributing to depression. Additionally, levels of neurotransmitters in the blood may not represent levels of neurotransmitters in the brain, which is extremely hard to measure. Neurotransmitter levels fluctuate greatly in the blood, which could be the result of neurotransmitters being produced by other parts of the body.

The chemical imbalance myth is thought to be perpetuated by drug companies. The companies advertise the chemical imbalance theory as fact to encourage consumers to buy their drugs. The myth has also been adopted by society as a way to take the blame of depression away from the person experiencing it. It states they have depression because there is a fundamental flaw in their biology. This helps to remove the stigma associated with the disorder, but it does not accurately represent the underlying biology.

In reality, what causes depression is much more complicated than an imbalance of chemicals. There are many environmental and genetic factors that can also play a role.

Depression Medications and Treatment

Depression treatment typically uses medications as well as therapy.

Many depression medications increase levels of serotonin and other neurotransmitters in the brain. They do this by preventing nerve endings from reabsorbing the neurotransmitter or preventing the neurotransmitter from being broken down. In either case, the neurotransmitter is more readily available to signal surrounding nerves. Some of the common medications used to treat depression include:

• SSRIs or selective serotonin reuptake inhibitors, which block the reabsorption of serotonin 
• SNRIs or serotonin-norepinephrine reuptake inhibitors, which block the reabsorption of serotonin and norepinephrine
• TCAs or tricyclic antidepressants, which block the reabsorption of serotonin and noradrenaline
• NDRIs or norepinephrine-dopamine reuptake inhibitors, which prevent reabsorption of norepinephrine and dopamine
• MAOIs or monoamine oxidase inhibitors, which prevent the breakdown of norepinephrine, serotonin and dopamine

Often, medication is not enough to relieve the symptoms of depression. In addition to medication, therapy can be highly beneficial. One example of therapy for depression is cognitive-behavioral therapy. The goal of this therapy is to modify the thought processes that might be contributing to depression.

There are also methods for chemical imbalance treatment without medication, such as exercise, diet and exposure to light. 

If left untreated, some people may turn to substances as a way to cope with depression. If you or a loved one is struggling with depression and substance addiction, The Recovery Village can help. To learn more about treatment plans, call today to speak with a representative.

Editor – Jonathan Strum

Jonathan Strum graduated from the University of Nebraska Omaha with a Bachelor's in Communication in 2017 and has been writing professionally ever since. Read more

Medically Reviewed By – Dr. Trisha Sippel, PhD

Dr. Sippel is a diversely trained scientist with expertise in cancer biology and immunology. Read more