Key Takeaways
- No one knows the exact cause; research points to many genes of small effect interacting with life events and differences in how brain circuits work.
- Family and twin studies put heritability somewhere around 60–85%, depending on the method, but most relatives of a person with bipolar disorder never develop it.
- There is no single "bipolar gene," and no genetic, blood or brain test can diagnose bipolar disorder.
- Stress, trauma, sleep loss and substances such as cannabis are better understood as triggers or risk factors in vulnerable people than as causes on their own.
Bipolar disorder has no single cause. The National Institute of Mental Health (NIMH) says the exact cause is unknown, but strong research shows it runs in families and that this is mostly explained by inherited genes, many of them, each adding a small amount of risk. Genes are not destiny, though: identical twins can differ, and stressful events, sleep disruption and substance use seem to influence when, and whether, illness appears in someone who is already vulnerable. This page explains what the evidence actually shows, including what genetic testing can and cannot do.
Is bipolar disorder genetic?
Yes, in large part. Bipolar disorder is one of the most heritable conditions in psychiatry. NIMH puts it plainly: people with certain genes are more likely to develop it, "many genes are involved, and no one gene can cause the disorder."
"Heritable" is easy to misread. It does not mean a parent passes bipolar disorder to a child the way eye color is passed down. It is a statistical estimate of how much of the variation in risk across a population is linked to genetic differences. A highly heritable condition can still skip a whole family branch, and a person with no known family history can still develop it.
The APA notes that the average age of onset is in the mid-20s, and NIMH says symptoms usually start in late adolescence or early adulthood. That timing matters for families: a teenager with a parent who has bipolar disorder is at higher risk, but the risk is spread across decades, and most children of affected parents do well. For a teen-focused view, see the guide to bipolar disorder in teens and children.
Why you see 58%, 85% and "70–90%": heritability explained
Search results quote different heritability numbers. They are all real, but they come from different study designs, so they are not interchangeable.
| Estimate | Study type | What it measures |
|---|---|---|
| About 85% (95% CI 73–93%) | Twin study: McGuffin et al., 2003, 67 twin pairs | How much more often identical twins (who share all their genes) are both affected than fraternal twins (who share about half). Twin samples are small and clinic-based. |
| About 58% | Swedish national family study: Song et al., 2015, 54,723 people with bipolar disorder | Risk patterns across millions of relatives in population registries. It also found first-degree relatives (parents, siblings, children) had about 5.8 to 7.9 times the risk of the general population. |
| "70 to 90%" | Summary range in the Merck Manual Professional | A reviewer's rounded range drawn from several studies, not a single new measurement. |
A fair summary: family and twin studies estimate heritability at roughly 60–85%. Registry studies tend to land lower than twin studies because they capture milder cases and a wider population. Either way, the message is the same: genes matter a great deal, and they are not the whole story.
The APA also reports that 80–90% of people with bipolar disorder have a relative with bipolar disorder or depression. That figure is the APA's own, and it describes people who already have the illness, looking back; it does not tell you the chance that a given relative will develop it.
Why there is no single "bipolar gene"
Large genetic studies show that bipolar disorder is polygenic: risk comes from many common gene variants, each with a very small effect. A 2013 review in The Lancet (Craddock and Sklar) named examples such as variants near CACNA1C, ODZ4 and NCAN, and described substantial genetic overlap with schizophrenia. No variant on its own predicts who will become ill.
This is also why "does bipolar skip a generation?" has no neat answer. With many small-effect genes reshuffled in every generation, a grandparent and grandchild can both be affected while the parent in between is not. That pattern reflects chance and environment, not a gene that switches off for one generation.
Brain-circuit differences
NIMH reports that the brain structure and function of people with bipolar disorder "may differ" from those of people without it, and that studying these differences may one day help predict which treatments work best. Researchers study it as a difference in how brain systems involved in mood, energy and sleep work together, not as a shortage or surplus of one brain chemical.
That older "one chemical out of balance" story is no longer how the field explains bipolar disorder (or depression). It is simpler, but it is not what the research shows, and it can make people feel their illness is either trivially fixable or a personal defect. Neither is true. A brain scan cannot diagnose bipolar disorder today; scans are research tools or are used to rule out other conditions.
Environment: stress, trauma, sleep and substances
Genes set the stage; life events often influence the timing. NIMH notes that people with a genetic risk may be more likely to develop bipolar disorder after trauma or other stressful life events. The evidence for several environmental factors looks like this:
- Stressful life events and trauma. Associated with onset in genetically vulnerable people (NIMH). Trauma does not "cause" bipolar disorder in someone without vulnerability, but it can be part of the picture and is worth discussing at an evaluation.
- Sleep loss. In a UK study of 3,140 people with bipolar disorder (Lewis et al., 2017), people with bipolar I were far more likely than those with bipolar II to report that losing sleep had set off an episode of high mood. This is about triggering episodes, covered in detail on our page on bipolar triggers and relapse warning signs.
- Cannabis. A 2026 meta-analysis of 19 longitudinal studies found cannabis use was linked to later bipolar disorder (relative risk 2.46). That is an association, not proof that cannabis causes it.
- Childbirth. The weeks after delivery are a known high-risk window for a first or recurrent episode in people who are vulnerable; see postpartum psychosis.
Medical and medication causes that can look like bipolar disorder
Some mood changes that look bipolar are driven by something else. NIMH notes that thyroid disease and some prescribed or recreational drugs can mimic or worsen mood symptoms, and the Merck Manual lists hyperthyroidism, stimulants, corticosteroids and dopamine agonists among the causes to rule out. Diagnostic manuals have separate categories for mood episodes caused by a medical condition or a substance, because the treatment is different.
This is one reason a careful evaluation includes a medical history, a medication and substance review, and labs ordered as needed. See how bipolar disorder is diagnosed for what that process involves.
Can a genetic test (including GeneSight) diagnose bipolar disorder?
No. NIMH states that no blood test or brain scan can diagnose bipolar disorder, and no genetic test can either. Because risk is spread across many small-effect variants, there is no gene panel that says "you have it" or "you will get it."
Pharmacogenomic (PGx) tests such as GeneSight answer a different question: how your body may process certain medications. For bipolar medications that information is narrower than many people expect. The FDA's pharmacogenomic biomarker table lists safety-related genetic markers for a few drugs (for example HLA-B for carbamazepine, oxcarbazepine and lamotrigine) and CYP2D6 for some antipsychotics, while lithium is not on the list. Our page on genetic testing for bipolar medication walks through what a report can and cannot tell you, and GeneSight testing at Willow & Stone explains the test itself.
What this means if bipolar disorder runs in your family
- Know the early signs of both poles: long stretches of low mood, and periods of unusually high energy with less need for sleep. The complete bipolar disorder guide covers the symptom picture.
- Tell any clinician who suggests an antidepressant about a family history of bipolar disorder. Antidepressant labels ask prescribers to screen for exactly this.
- Protect sleep and be cautious with cannabis and other substances, which are modifiable risks.
- If you are worried about yourself or your child, ask for an evaluation rather than relying on an online quiz. A family history alone is not a diagnosis.
At Willow & Stone, the first visit is a 90-minute evaluation that includes family history, a medical review and labs ordered as needed. Bipolar disorder treatment at Willow & Stone explains how care works.
Common Questions
Is bipolar disorder hereditary?
Largely, yes. NIMH says it often runs in families and that this is mostly explained by heredity. Family and twin studies estimate heritability at roughly 60–85%. Even so, most relatives of a person with bipolar disorder never develop it, and identical twins can differ, so genes raise risk rather than decide it.
If my parent has bipolar disorder, will I get it?
Not necessarily. A large Swedish study found first-degree relatives had about 6 to 8 times the general-population risk, which is a real increase, but most children of a parent with bipolar disorder do not develop it. Knowing the early signs and protecting sleep are reasonable steps; an evaluation is the way to answer the question for you.
Does bipolar disorder skip a generation?
It can look that way, but not because of a single gene turning off. Risk comes from many small-effect genes that are reshuffled each generation, plus environmental factors. A grandparent and grandchild can both be affected while the parent between them is not.
Can trauma cause bipolar disorder?
Trauma is not considered a cause on its own. NIMH notes that people who already carry genetic risk may be more likely to develop bipolar disorder after trauma or other stressful life events. Trauma history matters for treatment, so it is worth sharing at an evaluation.
What causes bipolar disorder in the brain?
NIMH reports that brain structure and function may differ in people with bipolar disorder. These are group-level research findings. They are not a single chemical deficit, and no brain scan can diagnose the condition in an individual.
Is there a genetic test for bipolar disorder?
No. No genetic, blood or brain test can diagnose bipolar disorder or predict it in a person. Pharmacogenomic tests such as GeneSight look at how you may process certain medications, which is a different question, and the information they give for most bipolar medications is limited.
Part of our bipolar disorder guide
Sources & Further Reading
- NIMH: Bipolar Disorder (NIH Pub. No. 25-MH-8088, revised 2025)
- McGuffin P et al. The heritability of bipolar affective disorder. Arch Gen Psychiatry 2003
- Song J et al. Bipolar disorder and its relation to major psychiatric disorders: a family-based study in the Swedish population. Bipolar Disord 2015
- Craddock N, Sklar P. Genetics of bipolar disorder. Lancet 2013
- Merck Manual Professional: Bipolar Disorders (Coryell, reviewed Jan 2026)
- American Psychiatric Association: What Are Bipolar Disorders?
- Sanjuan-Ortiz et al. Cannabis use and later bipolar disorder: meta-analysis. J Affect Disord 2026
- FDA: Table of Pharmacogenomic Biomarkers in Drug Labeling
This article is general education, not a diagnosis or advice for your situation. Do not start, stop, or change a medication without talking to the clinician who prescribes it; stopping a mood stabilizer suddenly can trigger relapse.
If you need help right now
Willow & Stone is an outpatient practice and is not an emergency service. If you or someone you care about is in immediate danger, call 911.
For urgent mental health support at any hour, call or text 988 to reach the Suicide & Crisis Lifeline, or text HOME to 741741 for the Crisis Text Line. Both are free, confidential, and available 24/7 nationwide.
Dr. Stacey Forbes, DNP, APRN, PMHNP-BC
Board-certified Psychiatric-Mental Health Nurse Practitioner and founder of Willow & Stone Integrative Mental Health. Nearly two decades of clinical experience; integrative, root-cause psychiatry in person in Arlington and by telehealth. Licensed in Texas, New Mexico, Florida, Alaska, Arizona, Colorado & Washington.
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