can depression turn into bipolar disorder

No, it is not possible

depression can’t turn into bipolar disorder. However, it is quite possible that your symptoms may be misdiagnosed as depression and then later correctly diagnosed as bipolar disorder.

In fact, according to a 2010 study headed by Dr. Charles Bowden of the University of Texas Health Science Center in San Antonio, about one-third of people who are initially diagnosed with depression may actually be suffering from bipolar disorder.