The exact causes for schizophrenia are unknown, but it is generally accepted that a combination of genetic and environmental factors may increase your risk of developing it. The use of drugs has been strongly linked to an increased risk as well.
The Role of Genetics in Schizophrenia
If you have an immediate sibling diagnosed with schizophrenia, there's an 8 percent chance you may get it, and 12 percent if one of your parents has it. The risk is highest if you have a schizophrenic identical twin, which is at 47 percent.1
However, genetics and family relations may not even play a role in developing schizophrenia at all, because 60 percent of schizophrenics do not have any relatives diagnosed with the same illness.2 Genetics is just one factor to be considered.
Environmental Factors That May Influence Your Risk
Several external factors have been linked to an increased risk of schizophrenia, including:
• Exposure to viral infections while inside the mother's womb
• Viral exposure during infancy
• Low oxygen levels during birth
• Physical or sexual abuse during childhood
• Early parental loss or divorce
Stress during pregnancy has also been linked to higher risks of schizophrenia once the child grows.3 Even other seemingly unrelated things, such as what season you were born and the location you grew up on, play a role.
Research suggests that you have a 10 percent higher risk of developing schizophrenia if you were born in the winter months in the Northern hemisphere. If you were born and raised in an urban environment, you have a 50 percent higher risk of developing schizophrenia.
Even Your Brain's Physical Properties May Play a Role in Schizophrenia
Since schizophrenia affects the way people view reality, it's natural that scientists compared the physical differences of a schizophrenic's brain to a normal person. What they've found is that chemical interactions between dopamine, glutamate and others may play a role in developing schizophrenia. Malfunctions during the production of these chemicals may increase your risk as well.4
Even the structure of your brain may play a role in schizophrenia. Brain ventricles, which are cavities filled with fluid that help keep the central nervous system healthy,5 are found to be larger in schizophrenics, suggesting a deficit in total brain tissue volume. A schizophrenic's brain is also found to have a few areas that have less or more activity compared to a normal brain.
Recreational Drug Use Has Been Linked to an Increased Risk for Schizophrenia at Later Ages
Recreational drug use at a young age has been linked with an increased risk for schizophrenia during the later years of life, especially among regular cannabis users.
In a study released in The The British Medical Journal (BMJ), over 50,000 soldiers from the Swedish Army were initially interviewed about their drug use, and were then regularly followed up. The study found that soldiers who heavily used recreational cannabis at the age of 18 have a whopping 600 percent higher risk of being diagnosed with schizophrenia in the next 15 years than those who didn't consume it.6,7
In a separate study conducted in New Zealand, teenagers by the age of 15 who used cannabis are 300 percent more likely to develop schizophrenia.8 It's inferred that your brain consistently grows during your teenage years, but it's also very vulnerable at the same time, which may explain the drastic risk increase.
While the evidence between drug use and schizophrenia is there, it is not accepted as an "official" cause of schizophrenia. That's because conducting official studies that encourage drug use on a person at risk of schizophrenia is very unethical.
Instead, researchers follow participants over a long period time by conducting cohort studies and regularly gathering information from participants.9 But based on the information provided, it's clear that avoiding recreational drug abuse can help lower your risk for developing schizophrenia.
In addition, note that these findings came from recreational cannabis users who have consumed high amounts over a long period of time. Controlled use of marijuana in a medical setting may actually be helpful for you, as researchers have found that it may help treat chronic nerve pain and promote better sleep.