Bipolar Disorder (BD) Overview^[condition] and NIH Women's Health Research

BD is a chronic mood disorder that is characterized by recurring episodes of mania or the less intense hypomania, depression, or mixed-mood states.^{1 , 2} During manic or hypomanic episodes, individuals may experience elevated mood, increased energy, and reduced need for sleep, while depressive episodes are marked by low energy, low mood, and loss of interest in daily activities.^{1 , 2} The main subtypes of BD are bipolar I disorder (BD-I), defined by manic episodes that last for at least 7 days and are sometimes accompanied by depressive or mixed episodes; bipolar II disorder (BD-II), which involves major depressive episodes combined with hypomania that lasts for at least 4 consecutive days; and cyclothymic disorder, which is characterized by milder hypomanic and depressive symptoms. Other specified and unspecified bipolar and related disorders are also recognized.^{1 , 2} Four or more episodes of mania or depression in a year is known as rapid cycling.

BD affects an estimated 40 million people worldwide, with prevalence estimates ranging from approximately 0.5% to over 1% of the global population.^{3 - 5} The causes are not fully understood, but research suggests that a mix of genetic, neurobiological, and environmental factors may be involved in the development of the disorder.^{1 , 6} Although BD can develop at any age, onset most commonly occurs during adolescence or early adulthood, with more than 70% of individuals showing clinical signs before age 25.^{1 , 6} BD is one of the most heritable psychiatric disorders and is associated with a higher risk of psychiatric and medical comorbidities, including cardiovascular disease, that exacerbate symptoms and contribute to premature mortality.^{3 , 5} Environmental factors, including childhood adversity, trauma or stressful life events, sleep disruption, and substance use, can also trigger or worsen mood episodes.^{1 , 3}

While BD-I has traditionally been considered equally prevalent in men and women, women receive a diagnosis of BD-II more frequently, and recent evidence suggests that BD diagnoses are increasing among women across all subtypes.^{5 , 7} Compared to men, women with BD more commonly experience rapid cycling, mixed-mood states, and irritable or dysphoric manic episodes, along with more frequent depressive episodes and a higher risk of suicide attempts.^{5 , 7} They also have higher rates of co-occurring conditions, including thyroid disease and anxiety disorders.^{3 , 7} Hormonal changes across the lifespan can also trigger or worsen mood episodes in women with BD.^{3 , 5} For example, 77% of women report increases in the frequency and severity of mood symptoms during perimenstrual, postnatal, or menopausal periods, and the first year postpartum is widely recognized as a high-risk period for BD relapse.^{8 , 9}

BD is diagnosed through a thorough psychiatric evaluation, as no laboratory test or imaging biomarker is currently sufficient to confirm the diagnosis.^{1 , 6} Because the symptoms overlap substantially with those of unipolar depression, attention-deficit/hyperactivity disorder (ADHD), and psychotic disorders, misdiagnosis is common, and many individuals wait years for an accurate diagnosis.^{3 , 5} Effective treatment typically combines mood stabilizers or atypical antipsychotics with psychosocial approaches, such as cognitive-behavioral therapy and psychoeducation.^{1 , 5} Lithium has the strongest evidence for long-term relapse prevention and for reducing suicide risk, which is much higher in people with BD.^{1 , 3}

The National Institute of Mental Health (NIMH) funds research on BD across the lifespan and partners with other NIH institutes, such as the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD), to advance understanding of the disorder. An NIH-funded study of more than 1.6 million women in Sweden found that women whose sisters had experienced postpartum psychosis, a rare but severe condition that is closely linked to BD, were nearly 11 times more likely to develop it themselves, highlighting the strong familial component.¹⁰ Another study that used Danish and Swedish national registers found that women with psychotic disorders who stopped taking antipsychotic medication during pregnancy were 60% more likely to have a severe relapse than those who continued treatment. The authors noted that lithium remains the medication with the strongest evidence for preventing relapse after childbirth in women with BD.¹¹ Complementing this work, the largest genome-wide study of BD to date identified 298 gene locations and 36 credible genes that are linked to the condition in an international sample of more than 158,000 individuals from diverse ancestries, a fourfold increase over previous findings. The study also found distinct genetic profiles for BD-I and BD-II as well as shared risk variants with schizophrenia and major depressive disorder.¹²