Why don’t we look at the data? I’m happy to translate any of the findings below for non-science folk:
EFFECTS ON THINKING: “CONCLUSIONS: Heavy marijuana use is associated with residual neuropsychological effects even after a day of supervised abstinence from the drug. However, the question remains open as to whether this impairment is due to a residue of drug in the brain, a withdrawal effect from the drug, or a frank neurotoxic effect of the drug.”
http://jama.ama-assn.org/cgi/content/abstract/275/7/521
CANCER: “Controlling for age, sex, race, education, alcohol consumption, pack-years of cigarette smoking, and passive smoking, the risk of squamous cell carcinoma of the head and neck was increased with marijuana use…”
http://cebp.aacrjournals.org/cgi/content/abstract/8/12/1071
OTHER HEALTH EFFECTS: “Conclusion: Marijuana and tobacco smoking each produces significant bronchial mucosal histopathology and the effects of marijuana and tobacco appear additive.”
http://www.chestjournal.org/cgi/content/abstract/112/2/319
SOCIAL EFFECTS: “RESULTS: Early adolescent marijuana use increased the risk in late adolescence of not graduating from high school; delinquency; having multiple sexual partners; not always using condoms; perceiving drugs as not harmful; having problems with cigarettes, alcohol, and marijuana; and having more friends who exhibit deviant behavior. These relations were maintained with controls for age, sex, ethnicity, and, when available, earlier psychosocial measures. CONCLUSIONS: Early adolescent marijuana use is related to later adolescent problems that limit the acquisition of skills necessary for employment and heighten the risks of contracting HIV and abusing legal and illegal substances.”
http://www.ajph.org/cgi/content/abstract/89/10/1549
ADDICTION AND WITHDRAWAL: “Abstinence from active marijuana increased ratings such as “Anxious,”“Irritable,” and “Stomach pain,” and significantly decreased food intake compared to baseline.”
http://www.springerlink.com/content/rjmym131861efryv/