I ain't namin' any names but:

"If you think marijuana is harmless, you might be suffering from the delusional tendencies caused by smoking pot, as revealed in a health study published in The Lancet on Friday (late July of 2007)...The research team, based in England, found that weed smokers have on average a 41 percent increased risk of developing psychotic disorders later in life. The heaviest users doubled their risk; yet even infrequent smokers had a modest increased risk. The findings imply that smoking marijuana may be the cause of more than 10 percent of schizophrenia cases. The analysis challenges the myth that ganja is no worse than alcohol and is safe to smoke in moderation. Although "most people who use cannabis will not develop such an illness," according to one of the study's author's, Dr. Stanley Zammit of Cardiff University, he warns that anyone developing mental problems or who has a family history of mental disease should punt the habit.

Zammit's group, led by Dr. Glyn Lewis of the University of Bristol, analyzed 35 published cannabis studies and controlled for confounding effects, such as personality traits that might be more of a determinant of psychosis than pot. Indeed, the researchers found that the habit was associated with psychosis—one of many risky behaviors seen among pre-psychotic patients—but it was not a direct cause of the disease in about half of the cases analyzed.

Carefully removing confounding factors, however, the researchers uncovered the first definitive cause-and-effect relationship. Cannabis use appeared to be the primary cause of several psychotic symptoms, from personality changes and disorganized thinking to hallucinations and serious disconnects with reality..