These two conditions are often confused, as they are both characterised by dramatic changes in mood.
Bipolar Disorder (also known as manic depression), is a cycling between two moods, not associated with their baseline personality: Mania and Depression. The cycles will last anywhere from weeks to months. Some people with Bipolar Disorder may be diagnosed with ‘rapid cycling’ bipolar, where their moods alternate at a quicker pace.
In Borderline Personality Disorder, the mood cycles are often much quicker than that of Bipolar Disorder, and may last anywhere from a few minutes to a week or two. Many people present with mood changes that occur within minutes or hours.
A key difference between the two is the basis that relationships have. People with BPD will find that their mood changes are manifested through interaction with others, or life events and triggers in one’s life routine.
People with Bipolar Disorder will find that their mood swings are not much related to life events or relationships.
Borderline Personality Disorder is comprised of both neurotic and psychotic mental processes. The thinking and behaviour of someone with BPD may exhibit more mental departures from reality or ‘dissociation’ – where feelings create facts.
However in people with Bipolar Disorder, the exhibiting behaviour may be more neurotic, where the mood swings may be focused on more extreme exaggerations of facts.
In people with Bipolar Disorder, the impulsive nature is only associated within the context of manic or depressive phases.
In people with Borderline Personality Disorder, the impulsive nature is a chronic presenting symptom.
It is important to note that BPD and Bipolar Disorder may be co-morbid (occurring at the same time), and it is possible for someone to be diagnosed with both BPD and Bipolar Disorder
Here is a table highlighting the differences: