Why might Post Traumatic Stress Disorder and Borderline Personality Disorder be Linked? 

Many mental health conditions can occur together within a single individual.  When two or more conditions occur together within one person at the same time, they go by the sad sounding term “co-morbid”. Now just because two events occur together it does not mean one causes the other for example there is a well-known link between high ice-cream sales and increased numbers of people drowning. A naive interpretation is that one causes the other so you shouldn’t swim after eating ice cream in case you drown.

The brighter among you will have spotted that one does not cause the other, but that there is a third independent factor which affects both, namely hot days. On hot days we are more likely to take part in reckless swimming, or the safer alternative, eat ice cream.

What has this to do with Borderline personality disorder and PTSD you may ask? It is an observable fact that many individuals with borderline personality disorder are also diagnosed as suffering from PTSD.   Many research hours have been devoted to trying to pin down what the causes this link, the hot sunshine to this particular melted ice-cream.  As yet there is no one agreed answer, but several possible explanations.

Doe the link lie in the origins of BPD and PTSD?

Most clinicians and researchers suggest that the origins of BPD often lie in some childhood trauma.   Sadly, this often includes prolonged exposure to abuse sexual, physical or emotional.  BPD typically begins in childhood. Trauma often precedes the development of borderline personality disorder. From these origins, the person with BPD often goes on to develop maladaptive coping skills to deal with what their mind tells them is a hostile environment.  Extreme volatility, impulsiveness, emotional excitability and extreme fears and jealousy are the acknowledged course of the condition.

PTSD on the other hand can occur at any stage in life but is more often the result of experiences in adulthood.  Like BPD it is a fairly new addition to the list of mentally debilitating conditions but has become increasingly recognized in veterans and people caught up in traumatic events.  Although only recently acknowledged as a condition, it has been around for years and was probably first catalogued by psychiatrists treating “shell shock” during the First World War.

So both conditions have their origin in the individual experiencing events with which their brain cannot cope.  The former is typically early onset and difficult to treat, because the full extent of the behaviors happen years after the event and may be well established before treatment is offered or sought.  The latter is equally difficult to treat but because of growing awareness following recent conflicts since 9/11, treatment is more quickly offered and available and therefore has less opportunity to become chronic.  So there may be a similarity with the origins but not the course of the illness, especially as PTSD is less stigmatized than PBD.

Is Borderline Personality Disorder a variant of PTSD?

Because PTSD and Borderline Personality disorders are often comorbid – existing together in the same person at the same time. Questions have been asked about whether the two are just variants.  That PBD is a variant of PTSD.  Research studies using large numbers of subjects with comorbid PTSD and BPD using personality inventories (specific questionnaires is designed to measure thoughts, feelings and behaviour)  suggest that while there is a possible but not conclusive association. (Gollier et al 2003).

The Possible Behavioral Predisposition

One of the key traits of BPD is reckless behavior.  This includes living to excess which may include a range of dangerous activities: driving too fast; sexual exploits with unfamiliar partners; drinking and drug misuse together with high risk sports and living on the edge. While there is no absolute certainty why any of these activities may cause a person to witness traumatic events, such activities increase the possibility.

BPD can increase the risk of traumatic events (e.g. car accidents and sexual or physical assaults) that may cause PTSD to develop. (Gollier et al 2003)

The Role Biological Factors

The growth of sophisticated technology has enabled the biological aspects of behavior to become increasingly clear.  We now know that there is a genetic predisposition for all manner of behaviours.  Brain chemistry controlled by genes, is involved in the development of gender identity, sexuality, and even a predisposition to certain behaviors such as addiction.

What is also known is that hormones also play a part and these may or may not be genetically influenced,  but by life events which trigger bodily chemical responses.  If such triggers are repeatedly experienced over a long period, they may influence the brain chemistry and cause permanent changes. The brain adapts to this.  It is a bit like a loud ticking clock when you are trying to sleep. At first you notice it and it may stop you sleeping. Eventually you adapt to it and sleep with it. If the clock stopped ticking you may then experience difficulty managing to sleep without it.  Without realizing you have become dependent on it.  So it may be with both PTSD and BPD.

One such effect is the so called fight or flight response.   In our ancestors the fight or flight response was a necessary biological tool of survival.  The release of adrenalin caused a cascade of chemical and neurological changes which prepared the body for to fight for its existence or run away.  The main problem now that, although we live in a sophisticated world our brain and hormones haven’t evolved at all and still react to those events which trigger fear in us in exactly the same way.  When someone shouts at you your body still responds in exactly the same way as an ancestor running from a sabre-toothed tiger.   Rinne et al (2004) suggested that  repeated abuse in childhood could permanently change the brain chemistry.  They quote the effects on animals of trauma when young and postulate that chemical changes caused by prolonged exposure to stress hormones during childhood may predispose people with Borderline Personality Disorder, to major depressive disorder and a greater susceptibility to PTSD.  This model however, does not perhaps explain the aetiology of PTSD without BPD. (Heffernan & Cloiter 2000).

 The Potential Role of Diathesis Stress Model?

This model is an attempt to explain why some people have an inherently greater weakness to developing certain conditions while others might be more robust in resisting them.   Predisposing factors are widely accepted in the physical health world – the relationship between family history and certain conditions such as heart disease, which can be a combination of genes, environment and lifestyle, is a good example.

In the case of PTSD and BPD it may be that life events, genes, environment could make a person more susceptible to the development of BPD and or PTSD.  The person could then suffer an adverse traumatic event which could in them trigger a PTSD response which in others would not.

If this model is a legitimate explanation then BPD caused by early life trauma may be the predisposing factor which might make some people more vulnerable to PTSD and therefore explain the comorbidity.


There is as yet, no one satisfactory explanation of the link between PTSD and BPD, nor may there ever be, or need to be.  Research continues.


  1. Julia A. Golier et al: The Relationship of Borderline Personality Disorder to Posttraumatic Stress Disorder and Traumatic Events Am J Psychiatry 2003; Volume: 160 pp2018-2024.
  2. Thomas Rinne et al: Hyperresponsiveness of hypothalamic-pituitary-adrenal axis to combined dexamethasone/corticotropin-releasing hormone challenge in female borderline personality disorder subjects with a history of sustained childhood abuse   Biological psychiatry Vol 52 Issue 11pp 1102-1112
  3. K. HEFFERNAN  &   M. CLOITRE A Comparison of Posttraumatic Stress Disorder with and without Borderline Personality Disorder among Women with a History of Childhood Sexual Abuse: Etiological and Clinical Characteristics Journal of Nervous & Mental Disease: September 2000 – Volume 188 – Issue 9 – pp 589-595

About Alexander Burgemeester

Leave A Comment...