Psychotic experiences are quite common even among people who don't have a mental health condition

Have you ever seen or heard something that turned out not to exist? Or have you ever thought something was happening that no one else noticed—perhaps thinking you were being followed, or that something was trying to communicate with you? If so, you may have had a psychotic experience.

The good news is, you're not alone. Psychosis, also called a psychotic experience or episode, is when someone perceives or interprets reality differently to the people around them. And it's estimated that around 5-10% of people will have a psychotic experience in their lifetime.

While they're different for each person, psychotic experiences often include hallucinations (seeing or hearing things that aren't there) or delusions (believing that something is happening that isn't real, or that others can't understand).

It's worth noting, though, that having a psychotic experience doesn't mean you have a mental disorder. Many people have these experiences without ever developing mental health problems.

Although hallucinations and delusions are characteristic of schizophrenia and some other mental health conditions, they are only considered to be a symptom of mental illness if the person is experiencing other symptoms of the condition, and if they're having a negative effect on a person's daily life. For example, other symptoms of schizophrenia include feeling less motivated, finding hobbies less interesting or enjoyable, and having trouble concentrating.

Given that psychotic experiences are a key symptom of schizophrenia, the underlying causes of them may be more closely related to developing schizophrenia than with other mental health conditions, such as depression. But it's also possible that the causes of psychotic experiences aren't at all related to those that cause schizophrenia and other major mental disorders.

There are still many questions about psychotic experiences that need to be answered. For example, we need to know more about the risk factors or causes of psychotic experiences. The relationship between these experiences and schizophrenia is also unknown. And, until now, it wasn't known to what extend genes influence a person's chance of having psychotic symptoms. Nor do we know how this relates to genetic contributions associated with developing schizophrenia and other mental health disorders.

Genes and psychosis

Our research has found some answers to these questions. We conducted the largest study of its kind using data from the UK Biobank study. We compared the genes and DNA sequences of 6,123 people who'd had a psychotic experience (but weren't diagnosed with schizophrenia or any other psychotic disorder), and 121,843 people who have never had one.

By comparing millions of DNA sequences from across the whole genome, we found that the likelihood of having a psychotic experience is determined by genetics to some degree—but the contribution is small.

This means that environmental factors may have a greater influence over genetics in causing isolated psychotic experiences in people without schizophrenia. For example, we know that using cannabis and having a traumatic experience, such as losing a parent during childhood, both increase the chances of having a psychotic experience.

The most important finding from our study is that many of the genes that were associated with psychotic experiences—particularly distressing hallucinations or delusions—were also associated with other mental disorders, which included, but were not limited to, schizophrenia. We found that the genetic risk for psychotic experiences was similarly connected with genetic risk for depression, bipolar disorder and neurodevelopmental disorders, such as autism and ADHD.

This study shows us that genes play a small role in the likelihood of having a psychotic experience. But this genetic contribution is shared with a broad range of mental health conditions—not specifically with schizophrenia. We now need to understand how these genes affect the risk of someone having a psychotic experience. And we need to understand the biological mechanism that causes these types of experiences.