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Reviewed by Jill Johnson, DNP, APRN, FNP-BC
Written by Our Editorial Team
Depression is one of the most common mental illnesses. In fact, according to the World Health Organization, an estimated five percent of adults worldwide, or 280 million people, are affected by some form of depressive illness.
Although depression is widespread, experts still aren’t aware of the precise factors that cause it to develop.
Some theories on the causes of depression revolve around risk factors, such as chronic stress, illness or a family history of depression.
Below, we’ve explained the basics of this theory, as well as how certain brain chemicals could play a role in the development of depression and other mood disorders.
We’ve also explained how common treatments for depression, such as antidepressants, work by targeting these chemicals to improve your moods, thoughts and behaviors and reduce the severity of depression symptoms.
Finally, we’ve shared what you can do if you’re feeling depressed and want to get help from a mental health professional.
Before we can get into the specifics of chemical imbalances and depression, it’s important to go over what these chemicals actually are, as well as what they do in the brain and body.
When you read about chemical imbalances and depression, the chemicals you’re reading about are most likely neurotransmitters.
Neurotransmitters are chemicals that allow neurons to communicate with each other. Your brain uses neurotransmitters to interact with other areas of your body, allowing it to perform a diverse range of important functions
You can think of neurotransmitters as your brain and body’s internal messaging system. At any given moment, your body relies on a range of neurotransmitters to handle things such as motor control, emotions, digestion and the function of your cardiovascular system.
Neurotransmitters are transported around your body through a process called chemical synaptic transmission, in which neurotransmitters are released from presynaptic neural cells to receptors inside postsynaptic cells.
Although it sounds complicated, the process works just like a management and communication system that allows different parts of your body to communicate.
Researchers haven’t yet worked out exactly how many neurotransmitters there are, but they’re aware that there are more than a hundred.
Each neurotransmitter transmits a different message and plays a unique but important role in managing your brain and body’s functions.
So, how exactly are neurotransmitters involved in mental health issues like depression? While some neurotransmitters are primarily responsible for controlling your physical functions, others play important roles in regulating your moods, thoughts and emotions.
Researchers have identified several important neurotransmitters that are involved in managing your moods and thoughts. Three of these are thought to be involved in depression.
The first neurotransmitter linked to depression is serotonin. Serotonin is a vital neurotransmitter (and hormone) that’s involved in regulating your mood, feelings of happiness and levels of anxiety. It also plays an important role in managing your sleep cycle, bone health and digestion.
Research suggests that low levels of serotonin are associated with depression, while high levels are associated with decreased arousal.
Low levels of serotonin are also linked to other mental health issues. For example, experts have found that people with low serotonin levels have an elevated risk of developing anxiety, suicidal behavior or obsessive-compulsive disorder (OCD).
The second neurotransmitter associated with depression is norepinephrine. Norepinephrine is also a hormone and a neurotransmitter.
It’s created in your adrenal glands and plays an important role in promoting alertness, attention and focus.
You may have heard of norepinephrine as noradrenaline. With adrenaline, norepinephrine plays a significant part in powering your cardiovascular system. It’s involved in important functions like blood pressure regulation and stimulating your heart.
Norepinephrine also has important mental functions. It’s involved in regulating your sleep-wake cycle, allowing you to wake up and function in the morning.
It also helps you to pay attention to specific tasks, remain focused on activities and form memories.
Like serotonin, norepinephrine can influence your moods. Sudden increases in norepinephrine can cause intense happiness and hyperactivity, but also panic attacks. Low levels may cause you to feel tired, unhappy and unable to concentrate.
Research has found that low norepinephrine levels are associated with numerous mental health issues, including depression, post-traumatic stress disorder and anxiety.
The third neurotransmitter linked to depression is dopamine. Dopamine plays a key role in your brain’s reward system.
Research has found that people’s dopamine levels are closely linked to their level of interest in completing certain tasks.
Put simply, dopamine is important for helping your brain decide which goals or tasks are worth the time and effort required to accomplish them.
Currently, research is mixed on the exact role of these chemicals in depression. While it’s clear that neurotransmitters play a key part in depressive illness, many researchers have challenged the idea that depression is solely caused by an imbalance of chemicals.
If you’re already familiar with the symptoms of depression, you may have noticed that many of them match up closely with the roles of neurotransmitters listed above.
Common depressive symptoms include:
A persistent sad, “empty” mood
Feelings of anxiety and worry
Thoughts of guilt or worthlessness
Suicidal thoughts and/or behavior
Fatigue and a general lack of energy
Difficulty falling asleep, staying asleep or waking up
Slow movement and/or speech
Changes in your appetite and/or weight
Physical aches, pains, cramps and discomfort
Reduced interest in hobbies and activities
Difficulty focusing on tasks or remembering information
Not all people with clinical depression have all of these symptoms. Some forms of depressive illness, such as seasonal affective disorder or bipolar disorder, may involve related symptoms that occur at specific times of year or in certain situations.
Our guide to depression symptoms provides more information on the signs and symptoms that you may notice if you have depression.
While research shows a link between different neurotransmitters and depression, many experts disagree that depression is caused solely by a chemical imbalance.
Other factors that may play a role in depression include brain structure, genes and exposure to certain depression triggers, such as stressful life events.
These factors all combine to affect a person’s risk of developing depression and other mental health issues.
You may have an elevated risk of developing depression if you:
Have a personal or family history of depression. Depression is recurrent, meaning it may come back if you’ve been depressed before. You may also have an elevated risk of depression if your family members have been affected by depression.
Have experienced a major life change, stress or trauma. Depression can start after losing a loved one, suffering a work-related setback or going through any other type of traumatic experience.
Have a physical illness or use medication. Some illnesses and medications can play a role in depression. You may feel depressed after finding out that you have an illness, or as a result of a change in your quality of life caused by an illness or injury.
Our guide to the causes of depression provides more information on the numerous factors that can play a role in depressive disorders.
If you’ve been formally diagnosed with depression, your healthcare provider will likely prescribe an antidepressant medication to help you control your symptoms.
Common types of antidepressants include:
Serotonin-norepinephrine reuptake inhibitors (SNRIs)
Norepinephrine-dopamine reuptake inhibitors (NDRIs)
As you can probably tell from the names of these drug classes, many work by targeting specific neurotransmitters involved in depression, such as serotonin, norepinephrine and dopamine.
For example, SSRIs -- the most common medications prescribed to treat depression -- work by increasing the level of serotonin throughout your brain.
This helps to reverse the effects of low serotonin, such as feelings of depression and anxiety.
Other antidepressants work by targeting different combinations of neurotransmitters. SNRIs, for example, target serotonin and norepinephrine, while NDRIs work by increasing norepinephrine and dopamine.
Antidepressants are effective, but they don’t work for everyone. Some people may need to try several different antidepressants before finding one that produces a noticeable improvement in their depression symptoms.
If you think you might be depressed, it’s important to seek help, whether it’s from a close friend or family member or from a mental health professional.
Try the following steps to manage your depression and make progress towards recovery.
Depression is a serious mental illness that often requires ongoing, expert treatment. If you feel depressed, one of the best things that you can do is to reach out to a mental health provider to talk about your options.
You can find help by asking your primary care provider for a referral, by searching for a mental health provider in your area or from home using our online psychiatry service.
If you’re diagnosed with depression, your mental health provider might prescribe medication to control your symptoms, recommend a form of talk therapy or suggest habits that may help you to improve the way you think, feel and behave.
If you don’t feel ready to contact a mental health provider, try reaching out to a friend or family member for help.
When you’re feeling depressed, it’s easy to isolate yourself. Simple things such as meeting up with a friend to spend time together or visiting your family for dinner can make a big difference to your mood and quality of life.
Depression often improves with changes to your lifestyle and habits. Try the following tactics to deal with depression naturally, either on their own or with medication and therapy:
Get plenty of exercise
Eat a healthy, balanced diet
Spend time socializing with other people
Avoid making major life decisions until you feel better
Focus on making steady, consistent progress, not getting better overnight
Keep your mental health provider updated about your progress
Scientific research shows a link between low levels of certain chemicals and the symptoms of depression, anxiety and other forms of mental illness.
However, this doesn’t mean that depression is as simple as a chemical deficiency. Depression, like other mental health issues, is a complicated disorder that can often develop without a clear cause.
If you’re feeling depressed, it’s important to get help. You can do this by talking to a close friend or family member, asking your primary care provider for a mental health referral or by using our online mental health services.
You can use our guide to major depressive disorder to learn more about depression symptoms, treatment options and more.