Marijuana contains many of the same cancer causing chemicals found in tobacco. In fact the amount of tar and monoxide inhaled is five times greater in every puff than cigarettes. That makes it contribute to respiratory problems for people who smoke it on a regular basis.
Not only does it cause respiratory problems but even marked deterioration in lung function after using it for so many years.
Marijuana users are likely to be low academic performers also. It causes problems with concentration and thinking. One study found that college students who used marijuana regularly had impaired attention and memory skills 24 hours after using the drug.
Good sport performance is difficult to achieve for someone with poor coordination caused by marijuana use.
Marijuana can cause increased anxiety, panic attacks, depression and even thoughts of suicide.
Users have impairment in sensory and time perception and are not safe drivers.
It also increases the likelihood of developing cancer of the head or neck.
Several studies with marijuana smoking workers have showed that they have more absences, tardiness, accidents, workers’ compensation claims, and job turnover.
Four out of twelve persons, age 12 and older have tried marijuana at least once in their lifetime and one out of ten reported using it within the last month. Chances are your child has tried it.

This is good information, thank you!  It seems like there are a lot of marijuana users who choose to dissociate themselves with these statistics, but there's no denying it.  Although marijuana may not be as harmful as other illicit drugs, it still is dangerous and better off not smoked!