cannabis can be very theraputic, but there are negatives that people simply don't account for. I made a post earlier in this thread about contaminants in cannabis and it didn't go over well, so I'm making the point again because it is incredibly important to account for. Don't take my word for it, educate yourself:
http://www.baycitize...cides-your-pot/
http://www.examiner....-and-pesticides
http://www.cannabism...t/contaminants/
http://www.hempfood....A/iha01205.html
http://adai.washingt...ntamination.htm
Cannabis usually has other compounds present in it, and that is a fact. The same thing happens with multi-vitamins, many are contaminated with lead and cadmium, and other toxic compounds. This is real people, and it cannot be ignored.
Nobody has ever died from smoking pot... I had a friend in high school who smoked a joint cut with pcp. She had a grand maul seizure and died. As far as she knew, she was smoking pot. Or, how about this:
"Recently in the United Kingdom there have been reports of glass beads being added from a spray to increase the weight of the plant and mimic the appearance of greater potency. Separate reports from Germany of lead particles being added to increase weight have also more recently appeared. These occurrences, although rare, are of great concern and have resulted in hospitalisations." (http://adai.washingt...ntamination.htm)
Based on this information, which all popped up after about 3 minutes of google searches, cannabis can be contaminated with fungus, mold, herbicides, pesticides, compounds to increase weight (LEAD and GLASS BEADS), and microbials. I can tell you from my personal experience that growers will practically water their plants with pesticides to keep the little black bugs off their crop. Pot is big $ for everyone involved, including dispensaries. This is real people, know whats going on here.
I wouldn't advise you vaporize pot of a sketchy origin. I would also never advise anyone to smoke pot, even good pot. Medical patients are advised to know their caregivers intimately, and to understand which lights and nutrients they use in their grows. There are some growers (particularly in medical states) who wouldn't touch chemicals besides organic nutrients and distilled water. Even then, some of the better growers water their plants with pure, distilled water for 2 weeks prior to harvest, thereby draining over 95% of the three macronutrients from the plants (nitrogen, phosphorous, and potassium) down the ionic gradient, and into the water...since most people shouldn't be ingesting high doses of combusted macronutrients.