Major Depressive Disorder

What is Major Depressive Disorder?

Major depressive disorder is one of the most common mental health conditions, but that doesn’t make it any easier to cope with.

By recognizing the signs and symptoms of the condition, you can seek help quickly and maximize the chances of a swift recovery.

Overview of major depressive disorder

Major depressive disorder (MDD) is a mood disorder which causes chronic low moods over long periods of time. For a diagnosis of MDD, an individual must have experienced a low mood for most of the day, almost every day, for at least two weeks, although the depression period can last for several weeks, months or even years if left untreated.

As one of the most common types of mental illness in the US, major depressive disorder affects 6.7% of the US population, which is around 15 million people. It can affect people at all ages, but the median age at onset of the condition is 32 years old. The condition is more prevalent in women than in men, but it may be difficult to accurately assess how many men have the condition since men tend to be less likely to seek help when experiencing depressed symptoms.

Major depressive disorder can have a significant impact on an individual’s lifestyle. The chronic low mood, fatigue and anhedonia (inability to get pleasure out of once enjoyable things) can have an impact on an individual’s ability to work and socialize. Career and relationships can, therefore, be put at risk when an individual has to deal with prolonged depression.

Suicide is also a major risk with depression, with experts estimating that up to 70% of suicide cases in the US being caused by major depressive or bipolar disorder, a condition which causes episodes of major depression. Depression causes people to experience intense feelings of worthlessness, hopelessness, and guilt which can spiral into thoughts of suicide and, in the worst cases, lead to suicide attempts. It is important to seek treatment for major depression as soon as possible in order to minimize the risk of suicide or suicidal ideation.

In cases where major depressive disorder persists for more than two years, doctors may diagnose persistent depressive disorder (PDD). Once known as dysthymia, this condition typically causes the same but less severe symptoms of major depression. It is perhaps the less severe symptoms which cause the depression to last for so much longer, because people are more likely to remain functional in their daily lives and simply find themselves feeling a little lower than usual, which they may not see as cause to visit a doctor.

Major depression can occur as part of bipolar disorder (BD), and in some instances, major depressive disorder is incorrectly diagnosed in individuals suffering from BD. Bipolar disorder causes dramatic shifts in mood between major depression and mania or hypomania, when the mood is significantly elevated. In some instances, individuals may have experienced episodes of major depression without yet experiencing manic episodes, which could lead experts to believe they simply have major depressive disorder. In other cases, individuals may not have even recognized elevated moods. This is particularly common with type II bipolar where individuals only ever experience depression and hypomania, which is a less extreme form of mania where individuals maintain a sense of control over their behavior and therefore don’t necessarily acknowledge that their mood isn’t normal.

Symptoms of Major Depressive Disorder

There is a wide range of symptoms of major depression, and according to the Diagnostic and Statistical Manual of Mental Disorders (DSM-V), individuals must have experienced at least five of the symptoms, for most of the day, almost every day, during the same 2-week period in order to be diagnosed with MDD.

Symptoms Major Depressive Disorder include:

  • Depressed mood
  • Anhedonia – diminished interest or pleasure in most activities
  • Significant weight loss without trying (more than 5% change in body weight within 1 month)
  • Insomnia (sleeping too little) or hypersomnia (sleeping too much)
  • Psychomotor agitation (agitated, restless movements, such as pacing) or psychomotor retardation (slowing of movement or speech)
  • Fatigue and low energy levels
  • Feelings of worthlessness or guilt without real reason
  • Reduced concentration and increased indecisiveness
  • Recurrent thoughts of death, suicidal ideation either with or without a plan, or suicide attempt.

Some may find the term “depressed mood” difficult to define, as this can feel different for everyone. However, common themes that tend to occur for people with depression are feelings of low self-worth and total hopelessness. They may have very low self-esteem, feel like a burden to others and struggle to feel happy, excited or content with any aspect of life. Although we all experience sadness and low moods from time to time, when it comes to major depressive disorder these feelings are experienced all the time and it can feel like there is simply no way out of the depressed state of mind.

It’s important to note that the symptoms of depression should not be clearly attributed to any other medical condition. For example, fatigue, hypersomnia, and poor concentration and decision-making are all symptoms of myalgic encephalomyelitis (ME) and depression. An individual experiencing these symptoms should not be treated for depression if they have already been diagnosed with ME.

Since depression tends to occur and worsen relatively slowly, individuals may not necessarily acknowledge that something is wrong. In these cases, it may be possible for friends and family members to spot depression in a person before they notice it themselves.

Symptoms to look out for include:

  • Frequent tearfulness
  • Unusual irritability
  • Sudden dramatic change in weight
  • Unusual pacing fidgeting or other agitated movements
  • Markedly slowed movements and speech

Causes of Major Depressive Disorder

Sometimes depression occurs as a result of a particular trigger or emotional trauma; this is known as reactive depression. Major and difficult life events, such as the death of a loved one, the loss of a job, financial difficulty or a tragic event such as a house fire or burglary, can all trigger depressed episodes. Although anyone would struggle to cope with these types of circumstances and experience low mood and feelings of hopelessness, if the diminished mood persists for most days over several weeks or months, individuals may require treatment for major depressive disorder.

In other cases, depression can occur with no obvious cause. In these instances, it is not always clear exactly why an individual experiences depression. Experts believe that there is a genetic factor involved in depression, and individuals with a parent or sibling who has struggled with depression are three times more likely to develop the condition themselves. However, there could also be an environmental factor at play, since children who see a parent or caregiver exhibiting depressive symptoms may learn to mimic that behavior later on in their life.

It is also believed that there could be differences in the brains of individuals who suffer from major depressive disorder with no known cause. It appears that a part of the brain called the hippocampus is smaller in those with a history of depression. Since the hippocampus has serotonin receptors, those with a smaller hippocampus have fewer receptors and therefore cannot process serotonin as effectively. Serotonin is one of several neurotransmitter chemicals which helps the brain to communicate and process emotions, so if this cannot occur normally, individuals may experience symptoms of depression.

In some instances, depression can also occur as a concurrent condition alongside other mental health disorders or physical illnesses. We mentioned previously that bipolar disorder involves periods of major depression, but the depression is actually a part of that disorder and therefore not a concurrent condition. However, in some mental health disorders, depression may occur concurrently as a result of the emotional stress that the original disorder causes. For example, individuals with schizophrenia, which causes psychosis, may become depressed as a result of the fear, confusion, and anxiety that they feel when experiencing psychosis.

People with chronic physical conditions may also become depressed due to having to deal with ongoing pain or discomfort, or due to them becoming frustrated that they cannot live normal lives due to their condition.

Treatments for Major Depressive Disorder

There are two primary methods for treating major depressive disorder: medication and psychotherapy.


There is a wide range of medications available known as antidepressants. These work to alter the balance of chemicals in the brain in order to generate a more stable mood. Usually, they take several weeks before they start having a positive effect, and they can make patients feel worse before they get better. They are designed for long-term use, and once a patient feels like they are back to their normal selves it is important to gradually wean off the antidepressants in order to avoid serious side effects.

Every type of antidepressant has a series of possible side effects which can vary in severity from person to person. Doctors may try a number of different medications and dosages until they establish a balance which has a positive effect on mood with minimal side effects. It may take a little trial and error before an individual finds a drug and dosage which helps them the most, since everybody is different and responds very differently to each medication.


Psychotherapy is often recommended alongside medication for successful treatment of major depressive disorder. Talking therapies can allow patients to share their thoughts and feelings in a safe, confidential environment and work through the problems or traumatic events that may have lead to their depression. It is also often helpful to try therapies such as CBT (cognitive behavioral therapy) and ACT (acceptance and commitment therapy) which can help individuals to find ways to manage the symptoms of depression by accepting or rationalizing unpleasant experiences or thoughts.

Prevention of Major Depressive Disorder

Sometimes depression can occur completely out of the blue with no real cause or warning signs. However, in order to reduce the risk of it occurring, particularly in those who are more at risk due to a history of depression or a genetic factor, the following tips may be helpful.

Visit a therapist or counselor

Rather than silently putting up with stress, anxiety, and low moods, it can be really helpful to share your feelings with someone else, particularly if you’re going through a traumatic or emotional life event. A therapist might also help you to recognize early signs of major depressive disorder so that you can seek treatment before the condition becomes very severe.

Exercise often

Exercise can help to alleviate stress and improve mood, so working out regularly might help to keep depression at bay. Low-intensity exercise such as yoga and Pilates can be particularly helpful in relaxing the mind while working out the body.

Establish your triggers and avoid them

By keeping a journal of your moods, you might be able to identify events, scenarios or circumstances which tend to trigger low moods. For example, you may find that you tend to feel low after getting too little sleep, and can then make a concerted effort to go to bed at a reasonable time each day.

Last Reviewed:
September 18, 2017
Last Updated:
September 18, 2017
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