
There is a myth out there that smoking marijuana is less harmful than smoking cigarrettes. Let's take into account effects for instance. On May 12, 2008, 51 students were taken into the hospital because their school driver crashed their bus -- apparently, she was high on marijuana. Yet there are some, that still argue, it is safe to use marijuana if you are "alone" since it doesn't harm anyone else and it doesn't really harm you.
Recent studies have shown that there is a dangerous side to marijuana that people tend to ignorantly set aside or they have not been educated on it yet.

Mental Illness
A combined study by Otago University, London's King's College and the University of Wisconsin in 2005 has shown that daily or monthly marijuana users had a higher chance of psychosis, specifically schizophrenia and other mental illness.
More Toxins than Tobacco
A study published in late 2007 by the Canadian health agencies has shown 20 times as much ammonia, a chemical linked to cancer. The study also found that there were five times as much hydrogen cyanide and nitrogen oxides, which are linked to heart and lung damage respectively. However, in the case of polycyclic aromatic hydrocarbons, the toxin linked to infertility, the researchers found concentrations were higher in cigarette smoke. In short, if you want poisons and cancer, marijuana is the way to go. For infertility, you have a better chance with tobacco.
Faster Lung Destruction Than Smoking Tobacco
A new study this year published in ScienceDaily clearly shows that bullous lung disease occurs in marijuana smokers approximately 20 years earlier than tobacco smokers. At present, about 10% of young adults and 1% of the adult population smoke marijuana regularly. Researchers find that the mean age of marijuana-smoking patients with lung problems was 41, as opposed to the average age of 65 years for tobacco-smoking patients.
Lead author Dr. Matthew Naughton says, "Marijuana is inhaled as extremely hot fumes to the peak inspiration and held for as long as possible before slow exhalation. This predisposes to greater damage to the lungs and makes marijuana smokers are more prone to bullous disease as compared to cigarette smokers."
The type of lung cancer damage is also harder to detect as it requires a CT scan and X rays often times cannot detect it. This paper is published in the January 2008 issue of Respirology.
A seperate study has estimated that one marijuana joint equals five cigarrettes worth of lung damage.
Heart Disease and Depression
A more recent study in May 2008 has shown marijuana links and ties to heart disease and depression. Long-term and chronic marijuana abuse has been associated with adverse effects on the heart, says lead author Jean Lud Cadet, a molecular neuropsychiatrist at the National Institutes of Health, but scientists are only beginning to understand how the drug's impacts the cardio- and cerebrovascular systems.
Summary
There's overwhelming evidence that tobacco causes cancer and is bad for your health. Studies upon studies show this.
Now the focus is on marijuana as researchers continue to pour dollars into tracking its adverse affects. It is still relatively a new area of research, one that most marijuana supporters cringe on -- the spotlight is now on the supposed "safe drug".