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What Is Major Depressive Disorder (MDD)?

Reviewed by: HU Medical Review Board | Last reviewed: September 2023

Being depressed often means having a low or saddened mood. However, the word “depression” can have a few meanings. It can mean a person’s current feelings. It can also refer to a group of mood-related symptoms called a syndrome. These symptoms can come along with a variety of mental health conditions.1

The word “depression” often is used to describe major depressive disorder (MDD). MDD is a mental health condition that involves having several symptoms of depressed mood for at least 2 weeks at a time. A person can have 1 episode of symptoms or multiple. MDD can greatly impact quality of life. MDD is also called unipolar depression or clinical depression.1-3

MDD is not the only type of depression. There are other kinds, too. These forms are diagnosed based on the exact symptoms a person has, when symptoms occur, and other factors. Some of the most common types of depression other than MDD are:1-4

  • Persistent depressive disorder (PDD)
  • Postpartum or prenatal depression (after birth or during pregnancy, also called peripartum depression)
  • Depression with psychotic features
  • Seasonal affective disorder (SAD)
  • Treatment-resistant depression
  • Premenstrual dysphoric disorder (PMDD)

Who gets MDD?

Anyone can experience MDD. It is very common. As many as 1 in 5 people in the United States will have MDD at some point in their lifetime. The average age of the first episode of symptoms is in a person’s 20s.5,6

Women are more likely to be diagnosed with MDD than men. However, all genders can be affected. MDD is most common in young adults, but it can impact kids and older adults, too.5,6

There are a few factors that might increase a person’s chances of being diagnosed with MDD. These factors include:2,3,5

  • Having multiple other medical issues
  • Having a lower income
  • Being divorced, separated from a partner, or widowed
  • Living in a more rural area
  • Using alcohol or recreational drugs
  • Having a family history of depression
  • Experiencing trauma or severe stress early in life

What causes MDD?

Experts do not know exactly what causes MDD. They think it may be related to several genetic, biological, environmental, and social factors.2,3

People with MDD often have changes in their neurotransmitters. These are chemicals that send signals to the brain and the rest of the body. They tell the body how to act, think, and behave. Neurotransmitters play a role in controlling many things, including mood, digestion, and movement.7

Common neurotransmitters thought to be affected in MDD are:2

  • Serotonin
  • Dopamine
  • Glutamate
  • Gamma-aminobutyric acid (GABA)
  • Norepinephrine

It is unclear whether these neurotransmitters themselves cause MDD symptoms or changes in the way the brain sends messages are the cause. It may be a combination of both. Processes in the brain that regulate hormones, thinking, and desire to seek pleasure play a role in balancing neurotransmitters.2

Environmental factors also can impact neurotransmitters. Examples of environmental factors include early childhood trauma or severe stress. Experiencing these issues can increase a person’s risk of developing MDD.2,8

Studies on MDD in families have shown that having a family history of depression in close relatives (like having a twin with depression) increases risk. This finding points toward a genetic or inherited cause of depression.2,8

What are the symptoms of MDD?

The exact symptoms of MDD vary in each person. Some are more severe than others, too. In adults, the main features of MDD may include:1-3

  • Having a low or depressed mood, including feeling hopeless, empty, or sad
  • Being unable to experience pleasure in activities, including things you once enjoyed (anhedonia)
  • Losing or gaining a lot of weight
  • Sleeping too much or too little
  • Moving slower or faster than everyone else around you (being either very restless or sluggish)
  • Feeling fatigued, tired, or weary
  • Feeling guilty or worthless
  • Having problems concentrating, thinking, or making decisions
  • Thinking about death (including planning or attempting to kill yourself or others)

How is MDD diagnosed?

Symptoms of depression can be caused by a few different things. Drug side effects, medical issues like thyroid problems, and more can all cause depression-like symptoms.9

There is no one blood test or imaging that a doctor can use to diagnose depression. Instead, your doctor will complete a full health history and physical exam. This will help them look for other medical causes of your symptoms. If no obvious medical issue is found, they will focus on psychological causes.9

Questionnaires that ask about mood are often used to screen for depression. An example of this is the PHQ-9 (Patient Health Questionnaire-9). It asks 9 questions about depression-like symptoms. If a person answers “yes” to multiple questions, they may have depression.10

Doctors use a book called the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5), to make an official diagnosis of MDD. According to the DSM-5, people need to have at least 5 symptoms from the above list on most days for at least 2 weeks. These symptoms must also interfere with daily life and impact their ability to function. One of the 5 symptoms needs to be a depressed mood or loss of pleasure.2

How is MDD treated?

In some cases, a primary care doctor can diagnose and treat depression. In others, especially more severe cases, a psychiatrist may be helpful. These are doctors who specialize in mental health conditions.11

Treating depression usually involves a combination of prescription drugs and talk therapy. Certain drugs can affect the balance of neurotransmitters like serotonin or dopamine. The most common medicines used to treat depression are:2,12

  • Selective serotonin reuptake inhibitors (SSRIs)
  • Serotonin-norepinephrine reuptake inhibitors (SNRIs)
  • Atypical antidepressants
  • Serotonin modulators
  • Tricyclic antidepressants
  • Monoamine oxidase inhibitors (MAOIs)

Each drug has its own benefits, risks, and side effects. These can vary based on factors such as a person’s age, health, and pregnancy status. You and your doctor will work together to figure out which drug options are best for you.12

Common types of therapy used in treating depression include cognitive behavioral therapy (CBT), family therapy, problem-solving therapy, and more.12

Some people have symptoms that do not respond to common drugs or therapies. This is called treatment-resistant depression. In treatment-resistant depression, other treatment options may be prescribed. These options include electroconvulsive therapy (ECT), transcranial magnetic stimulation (TMS), and vagus nerve stimulation (VNS).2,13

Other things to know

It can take a few weeks to months to start seeing improvements from prescription drugs. You and your doctor will work together to adjust treatment doses and drug types during this time. Some people need to try multiple different drugs before finding the right one (or combination).13

Overall, each person’s experience will be very different. Some people will have a single episode of symptoms that responds well to drugs or therapy. They may not need to be treated long-term. Others will have multiple episodes of symptoms over time. The severity of their symptoms or the length of each episode can change over time, too.13,14

People with MDD have a higher risk of worse overall health outcomes than those without MDD. This risk increases even more for those with other mental health or medical conditions.2

The symptoms of MDD can increase the risk of suicidal thoughts or actions. As many as 2 out of every 3 people with MDD will think about taking their life. Starting and sticking to a treatment plan can help manage symptoms. Crisis support options like the 988 Suicide and Crisis Lifeline (calling or texting 988) are available 24 hours a day, 7 days a week.2,15

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