Medically reviewed by Carina Fung, PharmD, BCPPS

What is clinical depression?

The question “What is clinical depression?” does not have as simple and straightforward an answer as one might hope.

According to the American Psychiatric Foundation1 (APA), depression, or major depressive disorder (MDD), is a mental health disorder characterized by a persistent depressed mood that lasts for at least two weeks.

But there’s a lot of room in this definition for ambiguity, as well as misinformation and misassumptions about depression.

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Updated research on depression treatments

Fortunately, awareness about depression is growing. With improving medication and breakthrough studies, we have a better understanding of what clinical depression is than ever before. We’ve also gotten much better at answering the question “What is clinical depression?”

Now, 80% to 90% of people suffering from depression can have a positive response to treatment if they stick with their plan. In fact, the APA has also found that, with treatment, nearly all patients can experience reduced symptoms of depression.

But before we look at the most common treatments, let’s first try to answer the question “What is clinical depression?”

Depression can be very complex

Chances are, you probably know at least one person who is currently depressed or has been depressed. But whether they were clinically depressed is a different story.

That’s because we use the word “depression” in English to refer to everything from economic principles to general feelings of sadness. But clinical depression is a very complicated and nuanced mental illness that does not fit easily into a single box or a strict set of definitions.

Some cases of clinical depression can be mild. Others can be much more severe. Clinical depression can range from small changes in your general mood (such as feeling down or sad) to no longer enjoying the things that once made you happy (such as not wanting to spend time with your friends or on activities you once loved).

Clinical depression can manifest in various ways, typically as changes to your appetite, sleep, thought process, or energy levels. It can even be existential: feeling like you’ve lost your purpose or meaning in life. In the most severe cases, clinical depression can lead to thoughts of suicide or not wanting to live anymore.

In short, different people can experience clinical depression differently.

We’ll go over the various symptoms later on, but the important thing to always remember is that, depression should not be taken lightly. It can affect you at work, at home, and when you’re with friends and family. It can keep you from sleeping and eating.

To this day, the exact definition of clinical depression is still being studied and debated by the medical community. We’re continuing to develop new and refined treatment methods.

And as treatments improve, our knowledge base grows, helping us better understand clinical depression.

The difference between sadness and depression

It’s important to note that being “sad” is not the same as being “depressed.” Depression has become something of a buzzword, especially among younger generations, which makes things more difficult for people who are actually clinically depressed.

Sadness is not a mental illness. Normal, healthy people experience sadness in their lives for a variety of reasons on a semi-regular basis. Life-changing events, like a loved one passing away or a divorce, can trigger deep feelings of grief and sadness. Even getting a lower-than-expected grade on a test could cause a student anxiety and sadness.

These types of events can cause anyone to struggle to enjoy the things they once did, especially if they once did these things with loved ones who are no longer present.

Even smaller events, like a disagreement amongst friends or a problem at work, can lead a normal, healthy person to feel sad, especially if they are highly sensitive or experience social anxiety.

The difference is that normal grief and sadness are often temporary and/or interspersed with feelings of happiness or joy. Some time after losing a loved one, you may think of them and smile or hear a story about them and laugh. You can still maintain a sense of confidence, purpose, and self-love.

Major depressive disorder (MDD)2, on the other hand, is typically associated with a day-to-day feeling of emptiness. As an example, you may feel that you don’t matter or that you don’t even like yourself. You may lose your ability to love yourself or fail to find meaning in the things you once cared about. Even your hobbies and passions may not make you happy anymore.

Unlike sadness, depression can be caused by an internal chemical imbalance or hereditary factors. But it can also arise for no discernable internal reason. As an example, depression has been linked to tragic life events that may also cause general sadness in anyone.

This is why depression can be difficult to diagnose or distinguish from other conditions, such as general feelings of sadness. That’s why it’s best to consult a doctor or psychiatrist to get a professional opinion if you believe you may be clinically depressed.

How common is clinical depression?

One thing to remember is that depression is a very common mental illness. How common? According to the Anxiety and Depression Association of America3 (ADAA), depression is “the leading cause of disability in the US for ages 15 to 44.”

To get a sense of how common depression actually is, consider this: about 1 in 15 adults will experience depression this year. But over the course of a lifetime, about 1 in 6 people will experience depression in some form, at some time.

Depression can start at any point in your life, but certain groups of people are more at-risk than others. People aged 18 to 29-years old are more likely to experience depression than those over 60. The average age of onset for depression is 32.5 years old. And if you’re female, you have a higher chance of experiencing depression than a male.

What are depression symptoms?

Depression can affect everyone in unique ways. Even though it’s classified as a “mental” illness, many depression symptoms actually affect a person’s body, as well. Some of the most common bodily symptoms of depression include:

  • Consistent feelings of sadness or a depressed mood
  • Loss of interest in activities that were once pleasurable
  • Irregular weight loss or weight gain
  • Trouble sleeping or oversleeping
  • Loss of energy and increased fatigue
  • Thoughts of suicide or suicidal ideation
  • Difficulty making decisions or concentrating; general inattentiveness
  • Feelings of excessive or inappropriate guilt or a general sense of worthlessness
  • A decrease in physical movement and exercise

Some people may have just one of these depression symptoms, while others may have multiple. Some of these symptoms can come and go, while others may stick around.

Also keep in mind from the previous section that, because conditions like thyroid disorders, vitamin deficiencies, and brain tumors can cause symptoms that closely resemble depression, these symptoms do not necessarily mean you have depression.

It is important to seek help from a provider if you are experiencing any depression symptoms so you can eliminate (or confirm) other medical conditions as the cause of your depression symptoms.

What are the causes of depression?

The causes of depression are not always clear. Medical experts are still working to understand the exact causes of depression, but in general, they usually fall into one of the following categories, laid out by the Harvard Medical School4.

Chemical and neural causes

For some people, there may be a chemical component to their depression.

Our brain contains a series of chemicals, like dopamine, serotonin, norepinephrine, and glutamate. Maintaining a certain balance of each of these chemicals can play a role in maintaining good mental health.

Conversely, if any of these chemicals becomes unbalanced, it may lead to the development of depression.

This is also true of the brain’s neurons. When they falter, they can produce inadequate levels of certain chemicals to certain regions of the brain, which can lead to depression as well.

Genetics as a cause of depression

Studies have shown that depression can actually run in families. While it may not be correlated as strongly as other genetic factors, there may still be a relationship.

As an example, some evidence shows that a person with a first-degree relative with depression may be 1.5% to 3% more likely to develop depression as well.

And for twins, genetics may be one of the more significant causes of depression. As we all know, identical twins share a genetic structure, so if one twin suffers from bipolar disorder, the other’s chance of developing the same mental illness may be between 60% and 80%. For fraternal twins, it may be closer to 20%.

Life events that trigger depression

Not to be confused with sadness or grief (as mentioned above), depression can be triggered by major negative life events, such as the loss of a loved one. A stressful event can also cause mental and bodily damage if it’s experienced over a long period of time.

Unlike grief and sadness, where a person experiences ebbs and flows in their mood, depression lasts longer than two weeks and is often characterized by self-loathing and feeling a lack of purpose.

Other medical problems that may lead to depression

Other medical conditions can have a powerful impact on our bodies and our chemical makeup. Some studies show that 10% to 15% of all depressions are caused by medical illnesses or medications.

Thyroid hormone imbalances5 and heart disease have both been connected to depression, as well as a host of other conditions. Some of these include stroke, dementia, certain immune diseases, HIV, and cancer.

Sometimes depression can be tied to nutritional problems, like B12 deficiency, or sexual issues like erectile dysfunction. Some of these conditions aren’t even classified as “depression” but rather depression can be a side effect of these conditions.

As you can see, depression is not usually caused by any one thing. And root causes might be multi-layered. For example, a patient who has a dopamine imbalance and FB12 deficiency may experience a tragic event and then develop clinical depression.

For these reasons, it’s best to seek medical help and get tested if you believe you may have clinical depression. And it’s important to explore your treatment options with a professional.

If you or someone you know is experiencing suicidal thoughts, call the National Suicide Prevention Hotline at 1–800–273–8255 or text HOME to the Crisis Text Line at 741741.

You may also reach out to the Samaritans: Call or text (877) 870-HOPE (4673).

Disclaimer: The information on this site is generalized and is not medical advice. It is intended to supplement, not substitute for, the expertise and judgment of your healthcare professional. Always seek the advice of your healthcare professional with any questions you may have regarding a medical condition. Never disregard seeking advice or delay in seeking treatment because of something you have read on our site. RxSaver makes no warranty as to the accuracy, reliability or completeness of this information.

If you are in crisis or you think you may have a medical emergency, call your doctor or 911 immediately.