[Prince]

-marijuana intoxication can cause distorted perceptions, impaired coordination, difficulty with thinking and problem solving, and problems with learning and memory

-Long-term marijuana abusers trying to quit report withdrawal symptoms including: irritability, sleeplessness, decreased appetite, anxiety, and drug craving

-A number of studies have shown an association between chronic marijuana use and increased rates of anxiety, depression, and schizophrenia

-marijuana smoke contains 50-70 percent more carcinogenic hydrocarbons than tobacco smoke

http://www.drugabuse.gov/infofacts/marijuana.html