What's behind suicide?

In researching this website, I came across some interesting studies and comments about what drives people to suicide. I thought it might be helpful to share this information so people can understand better what might be lying behind how they are feeling.
Research in the UK and in the US seems consistent in identifying the principal factors that contribute to someone committing suicide. According to the American Association of Suicidology¹, major depression is the psychiatric diagnosis most commonly associated with suicide. The risk of suicide in people with major depression is about 20 times that of the general population. About two thirds of people who complete suicide are depressed at the time of their deaths. That's a very high percentage.
The risk of someone suffering from an untreated major depressive disorder trying to commit suicide is around 1 in 5 (20%). However, the suicide risk among treated patients is around 1 in 1,000 (0.1%). That would point to treatment for depression substantially reducing the risk of suicide, so maybe there is hope for feeling better. See Help me.
Research studies^2,3,4 would point to the following being major factors triggering people to attempt to kill themselves. Note that more than 90 percent of people who die by suicide have the top two risk factors:

• Depression (especially if exhibiting extreme hopelessness, lack of interest in activities that were previously pleasurable, heightened anxiety and/or panic attacks) and other mental disorders
  
• An alcohol or substance-abuse disorder (often in combination with other mental disorders)
  
• Relationship difficulties (either with an existing partner, or due to divorce, being widowed or a relationship break-up)
  
• Prior suicide attempt (one study⁵ indicated that anyone who has previously attempted suicide is 100 times more likely to make a successful attempt compared to the suicide rate of the general population)
  
• Family history of mental disorder or substance abuse
  
• Family history of suicide, or exposure to the suicidal behaviour of family members, peers, or media figures
  
• Family violence, including physical or sexual abuse (especially for young people)
  
• Firearms in the home, the method used in more than half of US suicides
  
• Being in prison
  
• Unemployment
  
• Issues with studies (a major problem for those at university/college)
  
• Financial problems
  
• Legal problems
  
• Social deprivation
  
• Social isolation
  

However, suicide and suicidal behaviour are not normal responses to the factors mentioned above; many people have these risk factors, but are not suicidal. Research also shows that the risk for suicide is associated with changes in brain chemicals called neurotransmitters, including serotonin. Decreased levels of serotonin have been found in people with depression, impulsive disorders, a history of suicide attempts, and in the brains of suicide victims.
Depression, like other mental illnesses, is probably caused by a combination of biological, environmental, and social factors, but the exact causes are not yet known. For years, scientists thought that low levels of certain neurotransmitters (such as serotonin, dopamine, or norepinephrine) in the brain caused depression.
However, scientists now believe that the interplay of factors leading to depression is much more complex. Genetic causes have been suggested from family studies that have shown that between 20 and 50 percent of children and adolescents with depression have a family history of depression, and that children of depressed parents are more than three times as likely as children with non-depressed parents to experience a depressive disorder⁶.
In some people, there can be underlying physical reasons for severe depression. For instance, those diagnosed with a terminal illness, or those living with a long term physical disability, especially if accompanied by pain that is never likely to go away. It can be much harder to treat depression for people in this category, as the underlying causes are physical issues that cannot be cured. That isn't to say though that even people such as this can't find a motivating reason for living. See Help me.
For more information on the factors that lead to someone feeling suicidal, see Risk factors for suicide.

Sources

1. American Association of Suicidology, Factsheet: Some Facts About Suicide and Depression, 2009, from www.suicidology.org.
   
2. US National Institute of Mental Health (NIMH) factsheet: Suicide in the US: Statistics and Prevention, 2009 on www.nimh.nih.gov.
   
3. Hawton, K, Fagg, J, Simkin, S, Bale, E and Bond, A, (unpublished) "Attempted Suicide in Oxford 1995", University Department of Psychiatry, Warneford Hospital, Oxford.
   
4. K Hawton, D Casey, E Bale, A Shepherd, H Bergen and S Simkin, Deliberate Self-Harm in Oxford 2007. University of Oxford Centre for Suicide Research (from http://cebmh.warne.ox.ac.uk/csr/monpubs.html).
   
5. Hawton, K, "Suicide and attempted suicide", in Handbook of Affective Disorders.
   
6. U.S. Department of Health and Human Services. 2000. Mental health: A report of the surgeon general. Retrieved December 27, 2005, from www.surgeongeneral.gov/library/mentalhealth/chapter3/sec5.html.