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Like many psychological disorders, bipolar disorder is one for which we have a lot of stereotypes. We think of mood swings.

We imagine periods of deep depression and episodes of mania where a frenzied person thinks they're invincible or is all-consumed by their desire to achieve a goal. Popular media only reinforces these stereotypes, to the point where a lot of us probably don't have a very clear idea of what bipolar disorder is actually like. And like a lot of psychological disorders, bipolar disorder is much more complicated than we give it credit for.

Even psychologists continue to argue about how to define bipolar disorder—and whether it might be more of a spectrum than we used to think it was. But it might be ok that they're not sure. It might even help treat more people.

Bipolar disorder is divided into several subtypes in the DSM-5. That's the fifth edition of the Diagnostic and Statistical Manual of Mental Disorders, which sets out the criteria used in the US for diagnosing people with psychological disorders. There's bipolar I, which is the type we're most likely to think of when we think of bipolar disorder.

A person has to have at least one manic episode—in which they experience at least a week of their mood being abnormally elevated or irritated—to be diagnosed with bipolar one. During a manic episode, they might be obsessed with working towards a particular goal, have a grandiose sense of purpose, not need to sleep as much, or experience what's known as a “flight of ideas,” which is basically a racing mind. The most notable feature of bipolar II, on the other hand, are the periods of major depression.

Patients also experience periods of hypomania, which is a less extreme version of a manic episode. With the subtype known as cyclothymic disorder, a person experiences at least two years of depressive and hypomanic symptoms, but no major depressive or manic episodes. For kids, it's one year.

And the last subtype in the DSM-5 is “other unspecified bipolar and related disorders,” which sounds… pretty vague. But that's by design. This is where people with bipolar-ish symptoms that don't meet the full criteria of any of the other three can be categorized.

There's no cure for bipolar disorder, but it can be manageable with therapy and mood-stabilizing medication. It's also not totally clear what causes it, but there may be genetic factors involved. About 1% of the population has bipolar I, another 1% has bipolar II, and approximately 5% are estimated to have a milder subtype.

All that said, bipolar disorder is actually really tricky to diagnose. According to a 2013 study, only 20% of bipolar patients are diagnosed with a form of bipolar in the first year of seeking treatment, and the average delay between onset and diagnosis is five to ten years! Bipolar I is easier to recognize, because the patient is usually experiencing a manic episode when they seek diagnosis.

But bipolar II can be really difficult to tell apart from major depressive disorder. The difference usually comes down to whether or not the patient has a history of hypomania… but for someone who's often depressed, hypomania just might feel like a good or normal day. Researchers say that it's definitely possible that depressive patients who don't respond to antidepressants could actually have bipolar II.

And that could be really bad, because taking antidepressants without mood stabilizers can cause someone with bipolar disorder to switch to mania. And things only get more complicated from there. Some people with bipolar disorder have mixed mood episodes, which are when hypomania, depression, and/or mania get all smushed together.

And that's weird and confusing, for patients and researchers alike, because it basically flies in the face of the idea of bipolar as a disorder characterized by discrete episodes. There are also people who just experience hypomania, without any of the depression. And they often kinda like it!

They say it makes them super productive. A large clinical study published in 2011 has also suggested that hypomanic and manic episodes can be shorter than the widely-accepted four and seven days that are now used as cut-offs in the DSM-5. These shorter episodes, the researchers argued, should still count when trying to decide if someone has bipolar disorder.

And some researchers even believe that bipolar disorder can be progressive, although there's definitely not enough evidence to say for sure. All of this has led researchers to talk about bipolar disorder as a spectrum. The idea is that people can present with a wide variety of mild subvariants—and that many people's conditions might therefore have gone unrecognized.

And there's a lot of support for that way of thinking! But… even within the last decade, some researchers have pushed back on this idea. Some psychologists still advise a more conservative approach, to prevent overdiagnosis in the future.

The good news is that the DSM-5 leaves room for us to keep figuring this stuff out. That “other unspecified bipolar and related disorders” category we mentioned? It allows clinicians to continue to identify and diagnose patients who have subvariants that don't meet traditional thresholds.

And the DSM-5 specifically calls out “depressive episodes with short-duration hypomania” as a condition that should be studied further. Researchers have also called for additional research to pinpoint genetic or biomarkers that can help identify those with disorders on the bipolar spectrum with something more concrete than just the usual behavioral criteria. Ultimately, formal psychiatric diagnoses aren't about categorizing people for the sake of categorizing them.

They're about helping people to get the best treatment, and about making sure diagnoses are as accurate as possible to make future studies and future treatments more reliable. So while the definitions of bipolar disorder are still slippery... the DSM-5 is designed to accommodate that. And hopefully, as a result, we'll someday understand bipolar disorders and the bipolar spectrum better than we do today.

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