Methamphetamine, more popularly called meth, is a highly addictive drug that has been the thorn at the side of society. But among the long list of negative effects that the drug has to offer to its "host," researchers have shown that schizophrenia is another effect that people should be worried about.

The scientists from Toronto's Center for Addiction and Mental Health, or CAMH, found proof that heavy meth users have a higher risk of developing the mental illness.

In the study led by Russ Callaghan of CAMH, California hospital records of patients admitted between 1990 and 2000 were looked at. With over 42,000 meth cases, the researchers have discovered that people hospitalized for meth dependence had a 1.5 to 3-fold risk of being diagnosed with the mental illness compared to the other patients who used cocaine, alcohol, or opioid drugs.

Senior scientists and head of CAMH's Human Brain Laboratory Stephen Kish said that they still do not understand how meth and other drugs of that sort increases the risk of schizophrenia. Kish explained that the repeated use of meth and cannabis in some susceptible individuals triggers schizophrenia.

Just this October, a study led by Matt Jones of the University of Bristol's School of Physiology and Pharmacology studied cannabis and concluded that it can leave its users schizophrenic.

In Jones' study, he discovered that cannabis, or marijuana, disrupted the functions of the brain that are essential for memory and decision-making - something that is heavily implicated in schizophrenia.

These sorts of studies are done to improve modern medicine and to find a better way in treating those who are addicted to the substance.

Aside from the possibility of getting a mental disorder, meth users should be warned of other long-term effects such as violent and psychotic behavior, hallucinations, mood disturbances, delusions and paranoia, and homicidal or suicidal thoughts, reported Buddy T of About.com.