A chemical imbalance in the brain is said to occur when the brain has either excessive or insufficient chemical messengers, called neurotransmitters.

Some people claim that these imbalances can cause mental health conditions. However, most research now refutes the chemical imbalance theory.

Neurotransmitters are natural chemicals that help ease the communication between your nerve cells. Examples include norepinephrine and serotonin.

Some people claim that mental health conditions, such as depression and anxiety, result from a chemical imbalance in the brain. The hypothesis is sometimes called the chemical imbalance hypothesis or chemical imbalance theory.

However, it’s important to know that the chemical imbalance theory requires revision. Communication between neurons in the brain may play a role in the processes underlying depression.

However, much research states that an imbalance of neurotransmitters does not cause depression.

Structures within the brain, including the frontal lobe and hippocampus, regulate your mood and emotions.

Studies have observed changes in these parts of the brain, and the neurotransmitters within them, in people with depression and other mental health conditions. However, it’s unclear if these alterations cause conditions, such as depression, or result from them.

The limbic systems, a group of structures deep in the brain, are largely responsible for mood and emotional responses.

Regions of the brain involved in these systems include:

Neurotransmitters facilitate communication between nerve cells and target cells. Studies have linked changes in neurotransmitter activity with symptoms of depression.

A review of these studies found that reduced or abnormal activity of neurotransmitter systems within parts of the limbic systems may cause depression and anxiety.

However, the exact causes of depression and other mental health conditions remain unclear. Biological, psychological, and environmental factors may all play a part.

Scientists in the late 1950s proposed the chemical imbalance theory following the reversal of depressive symptoms with monoamine oxidase inhibitors (MAOis), tricyclic antidepressants (TCAs), and serotonin reuptake inhibitors (SSRIs) — all of which increased the concentration of neurotransmitters (dopamine, norepinephrine, and serotonin).

Research at the time focused on the role that chemicals in the brain play in depression and anxiety. These researchers hypothesized that insufficient levels of neurotransmitters could lead to symptoms, such as:

  • feelings of sadness, helplessness, worthlessness, or emptiness
  • overeating or a loss of appetite
  • insomnia or sleeping too much
  • restlessness
  • irritability
  • a feeling of impending doom or danger
  • lack of energy

While chemical changes in the body may occur during depression, research has not proven that these imbalances directly cause the above symptoms.

The chemical imbalance theory suggests that depression results from changing levels of neurotransmitters in the brain. The most common evidence used to support the chemical imbalance theory is the effectiveness of antidepressant medications.

These medications work by increasing the levels of serotonin and other neurotransmitters in the brain. Large-scale analysis shows that these medications are effective in treating symptoms of depression when compared with placebo.

However, while these medications can help improve a person’s symptoms, this doesn’t mean that the symptoms necessarily come from a chemical deficiency.

For example, serotonin plays a role in a person’s overall mental health, but there’s insufficient evidence to suggest that an imbalance in serotonin levels causes depression.

There are likely millions of chemical reactions occurring in the brain. The amount of reactions occurring at any one time makes it impossible to determine if someone is experiencing a singular chemical imbalance in their brain.

For example, there’s a time lag between when a person starts taking SSRIs, and when they reverse symptoms. This suggests that some other downstream process could be mediating the antidepressant effect.

There are no reliable tests to diagnose a chemical imbalance in the brain.

Doctors can perform tests to assess the levels of serotonin and other chemicals in your blood. However, this is not an accurate representation of the amount of these present in your brain.

A wide range of factors may contribute to a person developing depression. However, family genetics does appear to play a role.

Research shows that a family history of depression may increase a person’s risk for having it. While the importance of genetic factors in developing depression is not fully understood, twin and family studies suggest that the heritability of depression is roughly 37 percent.

Many smaller studies had identified genetic components that may be associated with depression. However, further, more conclusive research is required to fully assess the exact role genetics has in depression.

Learn more about the genetic component of depression here.

A health professional will typically assess your symptoms and take a medical history to diagnose mental health conditions.

They may also order blood tests to rule out other conditions, such as a thyroid disorder or vitamin deficiency. Both conditions can trigger symptoms of a mental health condition.

If these tests do not determine an underlying cause, your healthcare professional will likely refer you to a mental health professional, such as a psychiatrist or psychologist.

They will typically perform a psychological evaluation based on the “Diagnostic and Statistical Manual of Mental Disorders” (DSM-5) guidelines.

Learn more about how medical professionals diagnose depression here.

Several medications work by changing the levels of brain chemicals by blocking reabsorption.

Blocking reabsorption of specific neurotransmitters increases the level available for your nerves to use. This will activate your nerve receptors for a longer time.

Medications can alter the level of the following:

Some medications work on a combination of two more of the chemicals above.

Examples of these medications include:

  • Selective serotonin reuptake inhibitors (SSRIs). SSRIs work by blocking the reabsorption of serotonin. Examples are fluoxetine (Prozac), paroxetine (Paxil), and citalopram (Celexa).
  • Serotonin-norepinephrine reuptake inhibitors (SNRIs). SNRIs work by blocking the reabsorption of both serotonin and norepinephrine, leading to increased levels of these two chemicals in the brain. Examples include duloxetine (Cymbalta) and venlafaxine (Effexor XR).
  • Tricyclic antidepressants (TCAs). TCAs block the reabsorption of noradrenaline and serotonin. Examples are imipramine (Tofranil) and nortriptyline (Pamelor).
  • Norepinephrine-dopamine reuptake inhibitors (NDRIs). NDRIs, such as bupropion (Wellbutrin), block reabsorption of the neurotransmitters norepinephrine and dopamine.
  • Monoamine oxidase inhibitors (MAOIs). MAOIs block the reabsorption of norepinephrine, serotonin, and dopamine. These medications, including isocarboxazid (Marplan) and phenelzine (Nardil), are not as popular as other types of antidepressants.

While taking medications for a mental health condition, talk therapy techniques are also an important addition to your treatment plan.

Psychotherapy may help convert your thinking and behavioral patterns into healthier ones. Some examples are cognitive behavioral therapy and psychodynamic therapy.

During these therapy sessions, you will work with a mental health professional to use techniques to help you manage your depression or prevent it from returning once you’re feeling better.

There’s little evidence to determine that an imbalance in brain chemicals is the cause of any mental health condition.

If you’re experiencing any of the signs and symptoms of a mental health condition, it’s important to contact a healthcare professional for a diagnosis.

Don’t hesitate to find help that works for you.

Once you receive a diagnosis from your healthcare professional, you may need to try different treatments or combinations of treatments before finding the one that works for you.

Your healthcare professional will need to take into account several variables when determining a treatment plan. Patience is key. After finding the right treatment, most people show improvement in their symptoms within 6 weeks.