resize_shutterstock_468934322The question of whether drug abuse increases the risk of developing schizophrenia and other mental illnesses has been a hotly debated topic for decades. New research from Denmark that includes data from more than 3 million individuals takes an in-depth look at the scientific and clinical conundrum.
There has been a wealth of research on the impact that alcohol, cannabis, and other drugs might have on the risk of developing schizophrenia and other psychiatric disorders. However, it is a difficult area to study, and previous research has been controversial and often contradictory. As one example, many earlier studies could not take into account co-abuse; in other words, people who abuse a number of compounds.

Dr. Stine Mai Nielsen and Prof. Merete Nordentoft, from Copenhagen University Hospital, Mental Health Center in Denmark, recently embarked on one of the largest studies of its type. Their findings, presented at this year’s 2016 International Early Psychosis Association (IEPA) meeting in Milan, Italy, add another piece to this evolving and difficult puzzle.

This team of Danish investigators used data from 3,133,968 individuals born between 1955-1999 and available in nationwide Danish registers. In all, they identified more than 200,000 cases of substance abuse and over 21,000 schizophrenia diagnoses. Data was analyzed using a range of statistical measures; they also controlled for a number of factors including gender, urbanity, other psychiatric diagnoses, co-abuse, parents’ immigration to Denmark, parents’ economic status, and psychiatric history.

The investigators team found that abuse of any substance increased the risk of developing schizophrenia. The increased risks for developing schizophrenia with a number of other substances and drugs identified in this study were as follows:

  • Cannabis: 5.2 times risk
  • Alcohol: 3.4 times risk
  • Hallucinogenic drugs: 1.9 times risk
  • Sedatives: 1.7 times risk
  • Amphetamines: 1.24 times risk
  • Other substances: 2.8 times risk

The authors concluded from their trial that their results illustrate a robust association between almost any type of substance abuse and an increased risk of developing schizophrenia later in life. Although the results are clear, an age-old problem with the research remains whether it is impossible to prove whether the abuse caused the schizophrenia or vice versa. It is a possibility that someone who is predisposed to schizophrenia is more likely to abuse drugs; similarly, individuals could be susceptible to both developing schizophrenia and substance abuse. The authors note that the relationship between mental illness and drug abuse is likely to be incredibly complex.

In a second arm of the study, the same group of researchers at Copenhagen University Hospital, , examined the question of parental drug role and the risk of schizophrenia development. They wanted to identify whether parental substance abuse influenced the risk of schizophrenia. Parental drug abuse was split into two categories; diagnosed before birth and after. Schizophrenia diagnoses were taken from Denmark’s Psychiatric Central Research Register.

Both maternal and parental cannabis, whether diagnosed before or after birth, increased the risk of schizophrenia in the offspring. For mothers, it was associated with a six-fold increase and for the father a 5.5-fold increase in schizophrenia in the offspring. Related to alcohol’s risk, maternal abuse diagnosed before the birth of the infant was associated with a 5.6-fold increase in schizophrenia risk, but if diagnosed after the birth, this dropped by roughly 50 percent. Similarly, in fathers, pre- and post-birth risks were 4.4 times and 1.8 times greater, respectively.

The authors explain the potential reasons for the difference between cannabis and alcohol use. “Secondhand exposure to cannabis is apparently linked to schizophrenia. While it is easy to be exposed to secondhand smoke, with other substances, such as alcohol, there is no secondhand exposure, which could explain the much lower associations observed after birth for these substances.”

Although, as mentioned earlier, these studies cannot definitively tease apart the cause and effect, they are sure to add fuel to the fiery debate. Whether drugs cause schizophrenia or whether someone who is susceptible to schizophrenia is more likely to abuse drugs, unpicking the relationship and gaining insight into who may be most at risk is vital for early intervention and more successful treatment.

Readers of this blog are highly encouraged to read the complete story in the original new story from the link below. Additionally the reader and interested parties should access the complete research study data and author findings from the proceeds of the 2016 International Early Psychosis Association (IEPA) meeting in Milan, Italy. Lastly, interested parties seeking additional information and insights into the issues surrounding the linkage of substance abuse to risk of schizophrenia are encouraged to search the internet and other sources to identify the body of evidence in the scientifically published literature.