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 International Early Psychosis Association (IEPA) meeting in Milan, Italy, add another piece to the puzzle.
Schizophrenia and drug abuse
To dive into this question, the team of investigators used data from 3,133,968 individuals born between 1955-1999 from 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 team found that abuse of any substance increased the risk of developing schizophrenia. The increased risks were as follows:
Cannabis: 5.2 times
Alcohol: 3.4 times
Hallucinogenic drugs: 1.9 times
Sedatives: 1.7 times
Amphetamines: 1.24 times
Other substances: 2.8 times.