The main difference between unipolar and bipolar disorder is that extreme lows and major depression characterize unipolar disorder, whereas an alternating cycle of manic highs and extreme lows characterize bipolar disorder, states WebMD. They also differ in terms of affected gender and disorder prevalence.
Unipolar disorder, generally termed major depression, is almost twice as likely to affect women, advises WebMD. Bipolar disorder is equally likely to affect both men and women. Bipolar affects around 2.6 percent of U.S. adults, while unipolar is more prevalent; according to the National Institute of Mental Health, around 6.7 percent of individuals over the age of 18 suffer from major depression, with between 20 and 25 percent of adults suffering at least one episode in their lifetime.