Bipolar disorder causes emotional ups and downs, while depression causes a consistently low mood. The “bi” in the word “bipolar” means “two”. In bipolar disorder, you switch between two poles or extreme moods. Have very high moods (called manic episodes) and very low moods (called depressive episodes).
Bipolar disorder (sometimes called manic depressive) is different. If you have it, you have extreme mood swings. You experience periods of depression (similar to those of MDD). But you also have periods of great ups and downs.
Bipolar disorder and major depressive disorder are mood disorders. They are similar in that both include periods when you feel a bad mood or lack of activity in daily activities. Bipolar disorder, formerly called manic-depressive disorder, has periods of mania; depression doesn't. Both are serious mental disorders, different criteria for diagnosis, and both have effective treatments.
A relatively parsimonious idea is that bipolar disorder can be conceptualized as mania, with or without comorbid depression. At the same time, depression with and without mania could be seen as the same disorder. Mania and depression could be conceptualized as highly comorbid conditions, as could anxiety and depression. In the literature on anxiety and depression, most people conceptualize non-comorbid and comorbid depressions as parallel, with additional risk factors explaining the presence of comorbid anxiety.
A similar model could be applied to depression and mania, with depression conceptualized as the same disorder regardless of the presence of mania during life. Support for the “same model of disorder” would be derived from the absence of replicable differences in biology, course, symptomatology, or psychosocial history of bipolar and unipolar depression. Bipolar disorder is easily confused with depression because it can include depressive episodes. The main difference between the two is that depression is unipolar, meaning there is no period of “rise”, but bipolar disorder can include symptoms of mania or periods when you don't feel depressed.
A misdiagnosis such as unipolar depression is more likely to occur if a patient is evaluated early in the course of the disease, since the first episodes of mood in bipolar disorder are likely to be depressive. Given the abundance of patients with depressive illnesses presenting for treatment in primary care, it is certain that all primary care providers will be responsible for recognizing, diagnosing and treating diseases that are defined by depressive symptoms, including bipolar disorder. Major, or unipolar, depression is characterized by persistent periods of sadness, without the high manic phases of bipolar depression. People with bipolar II disorder often experience symptoms of depression or mania during a mood episode.
Seasonal depression is limited to a specific seasonal pattern, and most people experience symptoms in the fall and winter. However, despite methodological obstacles, distinguishing mania and depression as separate disorder processes would allow researchers to leverage the wealth of literature on unipolar depression in the design of treatments and etiological models of bipolar depression. No consistent differences have been found between the duration of the episode, although some studies suggest a shorter episode duration for bipolar depressions compared to unipolar depressions. And some people with bipolar disorder may also have additional conditions that make diagnosis and treatment difficult.
In a study in which patients were screened for bipolar disorder, only 18% of those who tested positive reported having received a previous clinical diagnosis of bipolar disorder; 42% received a diagnosis of something other than bipolar disorder, and 41% did not receive any diagnosis. To date, no study has directly examined whether people with a history of bipolar and unipolar depression are equally sensitive to relapse after a life event. Given the mix of symptoms and mood episodes in bipolar disorder, treatment with an FDA-approved medication that is effective in both the manic and depressive poles of the bipolar spectrum may be an advantage for patients. These studies also seem relevant to understanding the processes involved in generating and maintaining depressive and manic symptoms, since separate tests can be performed to contrast mania with depression.
When compared by the number of recurrences, bipolar II depressive episodes are associated with comparable levels of norepinephrine to unipolar depressive episodes. Unlike bipolar disorder, major depression is more common among women than among men, with a prevalence of 8.7 percent and 5.3 percent, respectively. In other words, some genes can lead to the development of bipolar disorder, while others can lead to bipolar disorder or unipolar disorder, depending on environmental influences. This unitary view of bipolar disorder codified a distinction between bipolar depression and unipolar depression, even though episodes of depression are common to bipolar and unipolar disorders.