I would like to briefly describe the three studies Ann Donnelly mentions in her Oct. 3 letter "Recognize high risk of marijuana."
First, the research linking tetrahydrocannabinol to schizophrenia is based on findings from administering volunteers with large doses of pure THC intravenously. Indeed, symptoms mirroring schizophrenia occur under such circumstances, but nobody is going to be injecting themselves with incredibly large doses of pure THC.
The study linking cannabis use to testicular cancer is taken from a small and isolated sample group (455 volunteers from Los Angeles County) and needs more research before any conclusions can be taken seriously (if there is a risk, it's probably minimal).
Finally, the study linking cannabis use to a lower IQ is valid, but overblown. While data do indicate that marijuana users experience a drop in IQ, the average drop was only eight points -- a hardly significant figure. Moreover, the drop is not proved to be permanent and most likely isn't. Furthermore, Professor Terrie Moffitt, a researcher involved in the IQ study, had this to say: "I'm fairly confident that cannabis is safe for over-18 brains, but risky for under-18 brains."
Do some research instead of simply reciting headlines.