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Actually, your pdoc is "up-to-date" regarding treatment. Within the last 5-7 years, research is suggesting that antidepressants do not help bipolar depression, and actually may make it worse. Bipolar depression is not the same as unipolar depression. (See the link to an article at the end)
Researchers are still investigating how antidepressants work on a bipolar brain, so there is no "gold standard" for treatment yet. But they are working on it, at least!
Many pdocs who are "up-to-date" still try antidepressants first, but if they do not work "immediately" they stop prescribing them and focus on increasing the mood stabilizer (lithium or lamictal) or the anti-psychotic (ex. seroquel works on mania and depression).
Lithium has long been known to prevent suicide and works moderately well as an antidepressant.
There is a huge "negative" stereotype and lack of understanding about Lithium. Even some of the comments here on PC are like "I would never try Lithium." "Lithium is so dangerous, you can die." The reality is that every drug affects the body.
Lithium is perhaps one of the most studied psychiatric medications because it has been around for-ever! A person can die from any medication if they overdose.
Compared with the "newer" medications today.... Think about Seroquel. So many people have been prescribed this medication, but the reality is that Seroquel is very harmful to the body. It causes weight gain and in many cases 50+ pounds, increased triglycerides, high blood glucose, etc, etc.
How is that better than Lithium?

**Sounds like your pdoc is good. I would be more concerned if pdoc kept trying different antidepressants when they do not work, because then I would question whether pdoc was up-to-date with bipolar treatment.
FYI: I am classic Bipolar 1 and
not on an anti-depressant. My main medications for bipolar are lithium and seroquel. My pdocs tried antidepressants years ago and nothing worked... which goes to support the new theories in research about our brains!
"Although antidepressant drugs remain the mainstay of treatment for unipolar major depression in both primary and secondary care settings, the evidence to support antidepressant treatment for bipolar depression is limited and increasingly controversial."
Antidepressants for Bipolar Disorder - Psychiatric Times