Bipolar Depression and Unipolar Depression: What’s the Difference?


Antidepressants are an extremely effective treatment for unipolar depression (major depressive disorder.). On the other hand, treatment of bipolar depression with antidepressants can be a problem. It can cause destabilization of mood, increase the rate of cycling between depression and mania, or actually precipitate a state of mania.

That being said, how does a clinician tell the difference between unipolar and bipolar depression when a patient presents with symptoms of melancholic mood, loss of interest in activities, slowing of thought processes, or changes in eating and sleeping habits?

Studies have shown that as many as 1/3 of patients with bipolar disorder are originally misdiagnosed as having unipolar depression. That is at least partially due to the fact that, statistically, most people with bipolar disorder experience depression, rather than mania, as their first symptom. It can also be the result of a missed diagnosis of mania, which is not always experienced as euphoria but is more frequently manifested as irritability, impulsivity, anger, aggressiveness or hypersensitivity.

There are, however, subtle differences between the two forms of depression that clinicians should be looking for.

Age of onset is one difference. Studies have shown that the younger the patient at the onset of symptoms, the more likely it is that bipolar disorder is causing the depression. Duration and frequency of depressed episodes are also clues. In bipolar disorder, depressed episodes are shorter and more frequent.

Another difference is family history. There is a clear genetic component to bipolar disorder. Unfortunately, it is sometimes difficult to be certain such a history exists, because the experience of mania can be so variable and reporting may be inaccurate. The presence of alcohol or drug abuse can be an indicator, as can troubles with the law. Troubles maintaining a job and problems with interpersonal relationships can also be common with bipolar disorder.

Those with bipolar depression often do not respond to antidepressants. Conversely, they might respond erratically or unpredictably, including agitation, insomnia, irritability or other forms of mania.

Perhaps the most critical consideration in managing the diagnostic process is the awareness that suicide is a much higher risk in bipolar than unipolar depression. Again statistically, suicide attempts are significantly more likely early in the disease process with bipolar depression than unipolar. The lethality of methods attempted is also much higher.

Recognizing the subtle differences between unipolar and bipolar depression is critical to the long-term treatment of the sufferer. Much study continues to identify the markers that will aid diagnosis.

Sources: Mood Institute,, National Institutes of Health and Psychiatric Times


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