Did Pot Trigger Giffords Shooting?

After horrific shootings, we hear calls for stricter regulation of guns. The Tucson shooting should remind us why we regulate marijuana.

After horrific shootings, we hear calls for stricter regulation of guns. The Tucson shooting should remind us why we regulate marijuana.

Jared Lee Loughner, the man held as the Tucson shooter, has been described by those who know as a "pot smoking loner."

He had two encounters with the law, one for possession of drug paraphanalia.

We are also learning that Loughner exhibited signs of severe mental illness, very likely schizophrenia.

The connection between marijuana and schizophrenia is both controversial and complicated. The raw association is strong:

• Schizophrenics are twice as likely to smoke marijuana as non-schizophrenics.
• People who smoke marijuana are twice as likely to develop schizophrenia as those who do not smoke.

But is correlation causation?

Increasingly experts seem to be saying: "Yes."

Time had a good summary of the expert view in an article published in July 2010.

Marie-Odile Krebs, professor of psychiatry at the National Institute of Health and Medical Research (INSERM) laboratory in France, and her colleagues published a study in June that identified two broad groups of people with schizophrenia who used cannabis: those whose disease was profoundly affected by their drug use and those who were not.

Within Krebs's study population of 190 patients (121 of whom had used cannabis), researchers found a subgroup of 44 whose disease was powerfully affected by the drug. These patients either developed schizophrenia within a month of beginning to smoke pot or saw their existing psychosis severely exacerbated with each successive exposure to the drug. Schizophrenia appeared in these patients nearly three years earlier than in other marijuana-users with the disease.

After the Tucson shooting, there may be renewed pressure to control the weapons that committed the crime. But what about the drugs that may have aggravated the killer's mental disease? The trend these days seems toward a more casual attitude and easier access to those drugs. Among the things we should be discussing in the aftermath of this horror is the accumulating evidence of those drugs' potential contribution to making some dangerous people even more dangerous than they might otherwise have been.

UPDATE: Read about the latest scientific research on the connection between Marijuana and Schizophrenia here.