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Major Depressive Disorder

Major depressive disorder is also known as clinical depression. It refers to having low mood, energy, and functioning for at least two weeks.

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Depression: Overview

Psychiatrist, Dr. Susan Samuels, explains what exactly is depression and what the symptoms might be.

Sanjai Sinha, MD profile image

Reviewed by Sanjai Sinha, MD

Updated on September 11, 2025

Clinical Depression is diagnosed when someone experiences depressive symptoms for two weeks or more. This sets the difference between depression and occasional feelings of sadness that one might experience every so often. Psychiatrist, Dr. Susan Samuels, explains what exactly is depression and what the symptoms might be.

The symptoms of depression include disrupted sleep, decreased level of interest, excessive sense of guilt, low energy levels, poor concentration, change in appetite, and suicidal thoughts. 

What happens in the brain when someone is depressed? Depression is thought to be caused by an imbalance in the neurotransmitters serotonin, norepinephrine, and dopamine. Neurotransmitters are naturally produced chemicals in the brain that are involved in sleep, mood, and anxiety. When people are depressed, their brain is not effectively using these neurotransmitters. 

References

American Psychiatric Association. (n.d.). What is depression?

National Alliance on Mental Illness. (n.d.). ECT, TMS and and other bran stimulation therapies.

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