Bipolar disorder (BPD) causes changes in a person’s mood and energy. These extreme and intense emotional states, or mood episodes, can affect their ability to function. People with bipolar disorder can have periods of normal moods as well.

Mood episodes are categorized into manic, hypomanic, or depressive. These mood episodes are marked by a distinct change in behavior. During a manic episode, someone can feel extremely energetic or irritable. Hypomania is less severe than mania and lasts for a shorter period of time. A major depressive episode can cause feelings of intense sadness or fatigue.

The Diagnostic and Statistical Manual of Mental Health Disorders V (DSM-5) lists more than four types of BPD. The three most common types are:

  • Bipolar disorder I: Manic episodes last at least seven days at a time, and symptoms can be so intense a person may need hospitalization. Depressive episodes may also occur, lasting at least two weeks.
  • Bipolar II disorder: This type has a pattern of depressive and hypomanic episodes without any intense manic episodes. It may be misdiagnosed as depression.
  • Cyclothymic disorder: This is a milder form of BPD. It involves alternating episodes of hypomania and depression. It lasts at least two years in adults and one year in children and adolescents.

Your doctor may diagnose you with another type of BPD, such as substance-induced, medical related, or unspecified BPD. These types may share similar symptoms, but have different episode lengths.

No single factor seems to be responsible for the development of BPD. But researchers are continuing to try and pin down the causes so that more effective treatments can be developed.

Research in genetics and BPD is fairly new. But more than two-thirds of people with bipolar disorder have a relative with either bipolar or major depression. Researchers are still trying to find genetic factors responsible for increased risk.

Inherited risk: Someone with a parent or sibling with BPD has a four to six times higher risk of developing it as compared to someone who doesn’t. An identical twin has a 70 percent chance of being diagnosed with BPD if their twin has it. Another review of twin studies found that there is a heritable component to BPD.

Bipolar and schizophrenia overlap: Researchers who study families and twins suggest that there may be a genetic link between BPD and schizophrenia. They also found that small mutations in specific genes appear to affect BPD risk.

ADHD overlap: One study found a genetic correlation between early-onset BPD and ADHD. Early-onset BPD occurs before someone is 21 years old.

Scientists are working to discover how the brains of people with BPD differ from the brains of people without BPD. Here are some notable discoveries.

Brain cells: The loss or damage of brain cells in the hippocampus can contribute to mood disorders. The hippocampus is the part of the brain associated with memory. It also indirectly affects mood and impulses.

Neurotransmitters: Neurotransmitters are chemicals that help brain cells communicate and regulate mood. Imbalances with neurotransmitters are linked to BPD.

Mitochondrial problems: Research suggests that mitochondrial problems may play a role in mental disorders, including BPD. Mitochondria are the energy centers in almost every human cell. If the mitochondrion doesn’t function normally, it could lead to change in patterns of energy production and use. This may explain some of the behaviors we see in people with psychiatric disorders.

Researchers who performed MRIs on the brains of people with BPD found elevated signals in certain parts of the brain. These parts help coordinate voluntary movement, suggesting abnormal cellular function.

Some scientists believe that environmental and lifestyle factors play a role in BPD. These factors include:

  • extreme stress
  • physical or sexual abuse
  • substance abuse
  • death of a family member or loved one
  • physical illness
  • ongoing concerns that affect your daily life, such as money or work problems

These situations can trigger symptoms or affect the development of BPD, especially for people who may already be at a high genetic risk.

BPD affects about 2.6 percent of the U.S. adult population every year. It equally affects genders, races, and social classes.

Age risk: BPD usually develops around age 25, or between the ages of 15 and 25. At least half of all cases are diagnosed before the age of 25. Some people do not develop symptoms until they are in their 30s or 40s, however. While it’s possible for BPD to develop in children 6 or younger, the topic is controversial. What may seem like BPD can be a result of other disorders or traumas.

Gender risk: Bipolar II disorder is more common in women than in men. But bipolar I disorder is equally prevalent in both sexes. It’s not known exactly what causes this difference in diagnoses.

Hormonal risk: Experts believe that thyroid hormones have major effects on brain function in adults. Depression and bipolar disorder are associated with abnormal thyroid function. The thyroid is a gland in the neck that releases hormones regulating growth and development. People with BPD often have hypothyroidism, or an underactive thyroid.

Certain factors can trigger manic or depressive BPD episodes. These factors increase the body’s stress level, which is also a trigger. Being familiar with your own personal triggers is one way to keep symptoms from worsening.

While triggers vary from person to person, some common ones include:

  • stressful life events, which can be positive or negative, such as the birth of a baby, a job promotion, moving to a new house, or the end of a relationship
  • disruption in regular sleep patterns, including decreased or increased sleep or bed rest
  • change in routine, like in sleep, eating, exercise, or social activities (structured routine can lower stress)
  • too much stimulation, like specific or loud sounds, too much activity, and caffeine or nicotine consumption
  • alcohol or substance abuse: overuse can cause ongoing bipolar symptoms, relapses, and hospitalizations
  • unmanaged or untreated illness

Read more: Bipolar disorder treatment »

With proper diagnosis, treatment, and management, it’s possible to lead a fulfilling, happy life with BPD.

Schedule an appointment with your doctor if you feel you have one or more of the signs of bipolar disorder. They can check your physical health and also ask you some mental health screening questions. If your doctor doesn’t find a physical problem for your symptoms, they may recommend that you see a mental health provider.

Your treatment will depend on your condition. It can vary from medication to therapy, and finding the right treatment can take some time. Talk to your doctor if any medication causes unwanted side effects. There are other options you can try.

Learn more from our living with bipolar disorder community »