What Is Major Depressive Disorder


You surely have heard about depression. In fact, taking into account that 280 million people have depression, a person close to you or even yourself might have suffered from this mood disorder.1 Even if this is true, how much do you really know about it?

Major Depressive Disorder (MDD) is a form of depression which, in contrast with the persistent depressive disorder, is not mild and chronic but severe and acute. This disorder is one of the most common mental health disorders worldwide and the leading cause of suicide deaths (being 60% of individuals who attempt suicide suffer from MDD or a severe depressive episode).2 These facts clearly illustrate how important it is to research MDD and to increase awareness of it. In reference to the last aspect, raising awareness of MDD is essential, mainly because it might help to increase the number of people suffering from MDD who seek professional help. In this way, this article will help you to increase your understanding of major depressive disorder and will hopefully help to solve any doubts that you may have about this common mental health disorder.

Understanding major depressive disorder

You might be interested in our dedicated article "Understanding Major Depressive Disorder".

Mood disorders, also known as affective disorders, are psychiatric disorders characterised by marked disruptions in emotions. There are different mood disorders, which can be classified as bipolar or depressive disorders, and as you can easily guess, MDD is a depressive one.3 The prevalence and incidence of MDD, as already mentioned, is considerably high. Indeed, different articles have demonstrated that the lifetime prevalence of MDD goes from 2% in China to 21% in France, meaning that, at some point, 2 to 21% of the population suffers from MDD.4 This means that up to 1 in 5 individuals might, sooner or later, have MDD. Many of these individuals try to deal with MDD by themselves as they feel ashamed or are worried about how people will react. This occurs because, in some cases, when patients talk about their situation with their relatives or friends, instead of being encouraged to ask for professional help, people around them misunderstand them and their disorder, increasing the individuals’ feelings of loneliness.5 Instead of being supportive and expressing empathy, which is what should be done, some people minimise their feelings and dismiss their symptoms, as they think that it is all in the mind and they are just lazy or not trying.5 In this way, increasing awareness is essential as knowing how to act when someone is depressed and realising that words can have a huge impact on people can be key to ensuring that people with MDD get the help they need on time.6

Causes and risk factors 

There are different factors that can lead to MDD or increase the likelihood of suffering from it. These factors include:

  • Biological factors:7
    • Genetic factors: research has demonstrated that genetics play a role in the development of MDD, being people more likely to suffer from this mood disorder if their blood relatives have MDD
    • Hormones and neurotransmitters: these chemical messengers are involved in causing or triggering MDD. As an example of a hormone, the excess of cortisol (also known as the “stress hormone”) caused by the hyperactivity of the HPA axis, has been linked to the development of MDD. On the other hand, in reference to neurotransmitters, research has suggested that changes in the action of neurotransmitters are involved in maintaining mood stability and play a role in MDD.
  • Psychological factors:7,8
    • Traumatic or stressful events such as sexual abuse or financial problems are considered to be risk factors for MDD.
    • History of other mental health disorders such as anxiety disorder or post-traumatic stress disorder
    • Having a negative self-concept or low self-esteem can also increase the likelihood of having MDD.
  • Social factors: there are many social determinants linked to MDD. This includes factors such as age, socioeconomic status, education, employment status, migrant status, ethnicity, and marital status.8 For example, MDD is more frequent among people with no degree-level education, while having a higher education has been associated with better mental health and lower depressive symptoms.9 Furthermore, it is worth mentioning that abuse of alcohol and recreational drugs is also a risk factor for MDD.7

Signs and symptoms7,10

MDD patients suffer from a variety of symptoms, with a depressed mood being the most common. The other signs and symptoms of MDD include:

  • Emptiness or hopelessness
  • Angry outbursts, irritability, or frustration
  • Loss of interest or pleasure (e.g. in hobbies)
  • Finding it difficult to concentrate, remember things, and make decisions
  • Having suicidal thoughts or suicide attempts
  • Self-harm
  • Avoiding contact with friends
  • Sleep disturbances
  • Changes in appetite and/or weight (they usually decrease but might increase instead)
  • Constipation
  • Slowed speaking and movement
  • Lack of energy
  • Unexplained physical pain (e.g. back pain or headaches)


If a doctor suspects that a patient might be suffering from MDD, they might want to carry out some tests to ensure that the symptoms are not being caused by underlying physical health conditions and to determine whether MDD is being caused by an underlying physical health problem (e.g. hypothyroidism). To do this, doctors might carry lab tests (e.g. blood tests to see if your thyroid is working properly) and physical exams. Apart from this, to make a diagnosis, mental health professionals might carry out a psychiatric evaluation and might use the criteria from the Diagnostic and Statistical Manual of Mental Disorders (DSM-5) from the American Psychiatric Association, which is a manual that establishes which symptoms are required for a person to be diagnosed with MDD.11

Management and treatment

Luckily, nowadays, there are both psychological and pharmacological treatments available. In reference to psychotherapies, Cognitive Behavioural Therapy (CBT) is one of the most effective. This therapy, which can be combined with medicines, is mainly based on improving awareness and understanding of depression, which helps patients to understand what they are going through and that they should not cope with it themselves.12

In reference to the pharmacological treatments, the most common drugs prescribed for treating MDD are: 13

  • Selective serotonin reuptake inhibitors (SSRIs) such as citalopram are usually the first line of treatment and the most commonly used antidepressants. 
  • Serotonin-norepinephrine reuptake inhibitors (SNRIs)
  • Atypical antidepressants
  • Tricyclic antidepressants (TCAs)
  • Monoamine oxidase inhibitors (MAOIs)

From these, TCAs and MAOIs are the less commonly prescribed drugs as they have a high incidence of side effects and lethality in overdose. Furthermore, to enhance the effect of antidepressants, these are sometimes given together with other drugs, such as mood stabilisers and antipsychotics.

Nevertheless, even though there are many treatments available, further research is needed, mainly because drugs have many side effects and are not effective in many cases. Thus, researchers are currently trying to find a treatment with rapid onset and few side effects.14


How can I prevent major depressive disorder

There are some strategies that may help to prevent MDD, as well as to cope with its symptoms. These include reducing and controlling stress (e.g. being physically active, having a healthy diet, and boosting your self-esteem15) and reaching out to family and friends.

When should I see a doctor?

It is recommended to see a doctor at the earliest sign of MDD. In this way, if you think you might be suffering from MDD, you should make an appointment either with your doctor or a mental health professional as early as possible. Furthermore, if you are having a severe depressive episode, having suicidal thoughts, or thinking about hurting yourself, you should call your local emergency number as soon as possible so that they can help you to feel better and give you their advice.


Major depressive disorder is a common mood disorder characterised mainly by a depressed mood. Apart from this, MDD also leads to other signs and symptoms, such as disturbing sleep, lack of energy, and changes in appetite and weight. There are different risk factors and causes of MDD, including biological (e.g. genetic factors), social (e.g. employment status), and psychological factors (e.g. trauma). Luckily, there are both psychotherapies (e.g. CBT) and pharmacological treatments (e.g. SSRIs) available. Further research is still needed so that drugs with fewer side effects and higher effectiveness can be found.


  1. WHO. Depressive disorder (depression) [Internet]. World Health Organization. 2023 [cited 2023 August 1]. Available from: https://www.who.int/news-room/fact-sheets/detail/depression#:~:text=An%20estimated%203.8%25%20of%20the,world%20have%20depression%20(1)
  2. Borenstein S, Nash AI, Dayal R, DiBernardo A. Patient-reported outcomes in major depressive disorder with suicidal ideation: a real-world data analysis using PatientsLikeMe platform. BMC psychiatry. 2020 Dec;20(1):1-1.
  3. Sekhon S, Gupta V. Mood disorder. Europe PMC. 2020 Jul
  4. Gutiérrez-Rojas L, Porras-Segovia A, Dunne H, Andrade-González N, Cervilla JA. Prevalence and correlates of major depressive disorder: a systematic review. Brazilian Journal of Psychiatry. 2020 Aug 3;42:657-72.
  5. Mongrain M, Shoikhedbrod A. When depression breeds rejection rather than compassion: Disagreeableness, stigma, and lack of empathic concern among support providers. Frontiers in Psychiatry. 2021 Jun 29;12:594229.
  6. Steger MF, Kashdan TB. Depression and everyday social activity, belonging, and well-being. Journal of Counseling Psychology. 2009 Apr;56(2):289.
  7. MayoClinic. Depression (major depressive disorder) [Internet]. Mayo Clinic. 2022 [cited 2023 August 2]. Available from: https://www.mayoclinic.org/diseases-conditions/depression/diagnosis-treatment/drc-20356013
  8. Remes O, Mendes JF, Templeton P. Biological, psychological, and social determinants of depression: a review of recent literature. Brain sciences. 2021 Dec 10;11(12):1633.
  9. McFarland MJ, Wagner BG. Does a college education reduce depressive symptoms in American young adults? Social Science & Medicine. 2015 Dec 1;146:75-84.
  10. NHS. Symptoms - depression in adults [Internet]. NHS. 2023 [cited 2023 August 2]. Available from: https://www.nhs.uk/mental-health/conditions/depression-in-adults/symptoms/
  11. American Psychiatric Association. Diagnostic and Statistical Manual of Mental Disorders (5th ed., text rev.). American Psychiatric Association. 2022
  12. Gautam M, Tripathi A, Deshmukh D, Gaur M. Cognitive behavioural therapy for depression. Indian journal of psychiatry. 2020 Jan;62(Suppl 2):S223.
  13. Bains N, Abdijadid S. Major depressive disorder [Internet]. StatPearls. 2023 [cited 2023 August 4]. Available from: https://www.ncbi.nlm.nih.gov/books/NBK559078/
  14. Karrouri R, Hammani Z, Benjelloun R, Otheman Y. Major depressive disorder: Validated treatments and future challenges. World journal of clinical cases. 2021 Nov 11;9(31):9350.
  15. Jacka FN, Berk M. Depression, diet and exercise. The Medical Journal of Australia. 2013 Oct 29;199(6):S21-3.
This content is purely informational and isn’t medical guidance. It shouldn’t replace professional medical counsel. Always consult your physician regarding treatment risks and benefits. See our editorial standards for more details.

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Susana Nuevo Bonastre

Bachelor of Pharmacology – BSc, University of Manchester

Susana is a pharmacologist with strong organizational and communication skills and a special interest in medical writing. For her final year at the University of Manchester, she did a project in science communication, for which she developed an e-learning resource to increase awareness of Major Depressive Disorder. Susana is currently finishing a taught Master’s in neuroscience and psychology of mental health at King’s College. Susana has experience as a mentor and as a medical writer at Klarity Health and, even though she is specially interested in mental health and psychopharmacology, she has also written articles related to nutrition and different diseases.

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