Is mental illness hereditary? What it means for marriage and having children

Is mental illness hereditary? The short answer

Is mental illness hereditary? The short answer: some mental illnesses run in families, and genes raise the vulnerability to them, but they do not make illness inevitable. According to the US National Institute of Mental Health (NIMH), in its publication revised in 2024, common conditions such as depression and anxiety most likely result from a mix of life experiences, environment and genetic differences. Having a close relative with a condition may raise your chance of developing it, but it does not necessarily mean you will.

The World Health Organization (WHO) lists genetics and substance use among the factors that can make a person more vulnerable to mental health problems, but it stresses that many people exposed to risk factors never develop a mental health condition, and that no single factor can predict on its own what will happen.

What does inherited risk mean, and why is it not destiny?

Don't look for a single "mental illness gene". NIMH explains that most genetic variations do not directly cause mental disorders, and that most of the genes linked to them raise the risk only by a small amount. In schizophrenia, for example, the UK's National Health Service (NHS) says no single gene is thought to be responsible. Instead, different combinations of genes make some people more vulnerable, and carrying these genes does not mean the illness will necessarily appear.

Be careful with "heritability" figures online

You may read that the "heritability" of a condition is very high and take it as the chance that your child will get it, but that is a misunderstanding. MedlinePlus, from the US National Library of Medicine, explains that heritability is a statistic describing how much of the variation in a trait, within a particular population and in a particular environment, comes from genetic differences. So a heritability of 0.7, for example, does not mean the trait is 70% caused by genes; it means that 70% of the differences in that trait between people in that population come from genetic differences. It is not the chance that you or your child will be affected.

And no test settles the question yet: NIMH states that genetic tests cannot currently predict the risk of developing a mental disorder accurately, and that tests bought without a doctor may give misleading results.

Genes and environment: what can wake up an inherited vulnerability?

Genes are one part of the picture; the other part is what a person lives through. Factors mentioned by health sources include:

• Stress and difficult life events: such as bereavement, divorce, losing a job and abuse. The NHS says they can trigger schizophrenia in someone already vulnerable but do not cause it on their own, and it counts them among the risk factors for bipolar disorder.
• A harsh childhood: WHO notes that harsh parenting and physical punishment can damage a child's health, and that bullying is a leading risk factor for mental health conditions.
• Drug use: covered in more detail below.
• Lack of sleep: which the NHS lists among the triggers of bipolar episodes.
• Pregnancy and birth complications: the NHS notes that people who develop schizophrenia were more likely to have had complications before and during birth, such as low birthweight, premature birth or a lack of oxygen during birth, which may have a subtle effect on brain development.

On the other side there are protective factors, including positive social interactions, good education and decent work, according to WHO. The UK's Royal College of Psychiatrists adds that growing up or living in a stable, positive environment may lower the risk of severe mental illness even when there is a genetic vulnerability.

Is depression genetic? And do bipolar disorder and schizophrenia pass to children?

How big the genetic role is varies from one condition to another, and the figures below are averages, not a verdict on any one person.

Is depression genetic?

MedlinePlus, in its page updated in 2018, notes that people with a first-degree relative who has depression (a parent, brother or sister) appear to have two to three times the risk of the general public. But many people who develop depression have no family history of it, and many people with an affected relative never develop it.

Is bipolar disorder hereditary?

The NHS says you are more likely to develop bipolar disorder if a parent, brother or sister has it. The Royal College of Psychiatrists, in its page published in 2020, explains that similar genetic risk factors are involved in bipolar disorder, severe depression and schizophrenia, and that having a parent with a severe mental illness is the strongest known risk factor for developing a severe mental illness yourself: their children have about a 1 in 3 chance. In other words, two out of three do not, and the figure is about severe mental illness in general, not one specific condition. Read more about bipolar disorder.

Will my child inherit schizophrenia?

According to the NHS in its 2023 review, about 1 in 100 people in the general population develop schizophrenia. If one non-identical twin develops it, the other has about a 1 in 8 chance, while an identical twin, who carries the same genes, has about a 1 in 2 chance. That means half of them do not develop it, so genes are not the whole story. Read more about schizophrenia and its treatment.

Is OCD genetic?

MedlinePlus says the inheritance pattern of obsessive-compulsive disorder (OCD) is unclear, and that the risk is higher among the first-degree relatives of someone with it, but most people who have a close relative with OCD do not develop it.

Why staying away from cannabis and stimulants matters if mental illness runs in your family

The US National Institute on Drug Abuse (NIDA), in its page updated in 2024, says there is some evidence linking cannabis (hashish or marijuana) use to an earlier onset of psychosis in people with genetic risk factors for psychotic disorders. It also notes that in some people cannabis can cause a temporary psychotic episode, especially at high doses, and that such an episode may be linked with developing a psychotic disorder later.

• The NHS says drugs, particularly cannabis, cocaine, LSD and amphetamines (the stimulant class that shabu, or ice, belongs to), can raise the risk of schizophrenia or psychosis, and that regular cannabis use in the teenage years and early adulthood is linked to schizophrenia later on.
• The NHS also lists cannabis and cocaine among the risk factors for bipolar disorder, and NIDA points to research that found a higher risk of depression among people who used cannabis in adolescence.

Research has not yet settled whether drugs directly cause these illnesses: the NHS says this is unclear in people who are susceptible to schizophrenia, and NIDA explains that genetic and environmental factors affect both mental health and drug use. But the practical message is the same: if schizophrenia, bipolar disorder or psychosis runs in your family, staying away from cannabis and stimulants is a clear step to protect yourself and your children. And if you think of cannabis as "light", read is hashish addictive?

Marrying someone with mental illness: what really matters?

A psychiatric diagnosis does not decide the future of a marriage on its own, and the absence of one does not guarantee success. What matters more than the name of the condition is how it is managed. These questions can help before an engagement:

• Is the diagnosis clear? And does the person see a psychiatrist regularly?
• Have they been stable for a while? And do they know their own early warning signs of relapse?
• Do they stick with treatment? Without stopping or changing their medicine on their own.
• Do they stay away from drugs? Drugs are risk factors for psychosis and bipolar disorder, and the NHS notes that they can cause a relapse in someone who has had psychosis before.
• Are both families supportive? A stable environment may protect.

Honesty before marriage

Some people fear that telling the other side will end the engagement, so they hide the illness or stop their medicine before the wedding. But hiding it destroys trust if it comes out later, and stopping treatment without the doctor can put the person at risk of relapse. Better is an honest, calm conversation at the right time, and the two of you can attend an appointment together with the treating doctor, with the consent of the person who has the condition.

The decision stays with the couple and their families. Medical information belongs to the person it concerns, so their reports should not be requested without their permission.

Planning to have children: how can a family lower the risk for the next generation?

Nobody can change their genes, but a family can change a lot about the conditions children grow up in:

1. Plan pregnancy with the psychiatrist in advance: the Royal College of Psychiatrists advises women with bipolar disorder to discuss pregnancy plans with their psychiatrist beforehand, because some mood stabilizers are not suitable in pregnancy. No medicine should be stopped or changed without the doctor. For more detail, read our article on psychiatric medication in pregnancy and breastfeeding.
2. Know the risk of postpartum psychosis: the NHS says it is higher in women with bipolar disorder or schizophrenia and in those with a family history of mental illness, and it advises specialist care during pregnancy and a clear plan for after the birth.
3. Provide a stable, safe home: without harsh parenting or physical punishment.
4. Reassure children when a parent is ill: the Royal College notes that children may think they are to blame, so they need reassurance and a steady routine.
5. Talk to your children about drugs early, and keep an eye on them without excessive worry: not every bout of teenage sadness is an illness, but a clear, lasting change deserves an early assessment.

When do you need a specialist assessment rather than internet figures?

General figures may reassure or frighten you, but they cannot answer the question of your own situation. Book an appointment with a psychiatrist if:

• You are thinking about marriage or children, and schizophrenia, bipolar disorder or another severe mental illness runs in your family or your partner's
• A wife takes psychiatric medicine and is planning a pregnancy or has found out she is pregnant
• You notice lasting symptoms in yourself or one of your children, such as sadness that won't lift, sharp swings in mood and sleep, or obsessions that disrupt daily life
• Someone in a family with mental illness has started using cannabis or stimulants
• You are offered a commercial genetic test that promises to reveal your "mental health risk"

Before the appointment, gather what you can of your family history: which relatives were affected, with what condition, and how they were treated. NIMH advises writing this down and sharing it with your doctor.

How can an assessment at Oxygen Center help?

A psychiatrist does not read your future from your genes, but they assess your situation, understand your family history and explain what the figures mean in your case. At Oxygen Center the path usually starts with an appointment with a psychiatrist at the outpatient clinic, for men and women aged 15 and over (under 18 with a parent or guardian's consent). If you need support to get past the worry or to cope with an illness in your family, psychotherapy sessions can help.

Families can come alone first to ask questions and understand, even if the person with the condition is not ready yet. And if you'd like to start with a simple question, contact us at any time.